Hi A98Alvin--Happy New Year, and welcome to EpicSki!
You are not a beginner, by any stretch of the imagination, even if you are just starting to work on bumps. You've got all the tools you need--well-timed pole plant, and the ability to make quick turns. To your specific question, though, you are NOT chronically skiing in the back seat, and the aft position of your hips is not an indication otherwise. LiquidFeet gave you some great ideas to work on, and I'll just reiterate: your basic fore-aft "stance" is not a problem, but you will need to add some vigorous and accurate fore-aft movements of your feet, as well as up-down movements (flexion-extension) of your legs, to enhance your ability to absorb the bumps--as shown in the "StickMan" "backpedal" animation.
It all happens quickly, especially at the speed you're going in those bumps, so you don't have time to think about it much. But if you can simply visualize your feet moving in more-or-less circles beneath your body--as the animation shows--it should help smooth out your bump absorption. That will keep your feet in smoother contact with the snow, and enable you to better manage your turn shape and speed. Add the enhanced steering movements that LiquidFeet described, and you'll be able to take your technique to bigger and bigger bumps on ever steeper terrain.
You can work on these movements by traversing across a big bump field, if you can find one at your area (this won't work on the narrow artificial bump run in your video). Ski across the bumps, focusing on following the terrain with your feet while minimizing any up-down movement of your body (center of mass). Visualize the "backpedaling" motion. Find "center" to start--press firmly forward on your boot tongues, then move your body (hips, shoulders, etc) slowly back until you lose all pressure on, but not contact with, the tongues. Try to maintain this contact-but-not-pressure on the tongues as you traverse the bumps--which will require very accurate fore-aft movements of your feet beneath your body. Keep practicing, increasing speed as your comfort and confidence improves.
Combine these absorption movements with turns in the bumps, without changing the timing of the flexion-extension movements (in other words, stay "low" and compressed on top of the bump, then extend your legs down into the trough). All of this may take some practice. The natural motion that most people have at first is just the opposite--they extend on top of the bump, and compress in the trough between the bumps, especially when they start adding in a turn. It's not always an easy pattern to break. If you have trouble with it, I strongly encourage you to find a good instructor and take a lesson or two.
Finally, regarding your original question and the title of your thread, it's worth looking again at those hips. Note that as your hips move aft, you stretch your upper body and arms forward (easily seen in LiquidFeet's stills pulled from your video). This compensating forward movement of your upper body keeps your center of mass over your feet, even though the hip position may make it look like you're "in the back seat." You are not as aft as you think you are.
But there may be a problem with your boot setup. Notice how upright (vertical) your shins tend to be, and how little flex you have in your ankles. How stiff or soft are your boots? How snug are they around your lower legs? If they are loose and/or soft, then the problem is one of movements that you should be able to change (and you may want to consider snugger, stiffer boots). If they are already snug and stiff, such that they hold your leg rigidly in that upright and open-ankle position, they may need some attention to dial in the forward lean. When your lower legs (shins) are too upright (for whatever reason), they move your hips back, requiring you to compensate just as you do by bending your upper body forward.
Here's an illustration that shows how fore-aft boot setup can affect your basic stance:
Notice that all three skiers in the first column are similarly centered over their feet, but they need to adopt different postures to accomplish that. The first skier (A1) is optimally aligned fore-and-aft (one sign is that the shins and spine are pretty much parallel in this "neutral," slightly flexed position). Your posture resembles skier B1, whose ankles are extended and shins are very upright. The problem with this setup is not that it necessarily puts you in the proverbial "back seat" (you're still balanced in B1), but that it interferes with your range of motion, preventing you from flexing deeply without losing your balance--see figure B3.
So, whether it's the effort to flex your ankles a bit more (and bring your upper body more upright), or a boot adjustment to dial in more forward lean, one way or another you would probably benefit by looking more like A1 when standing in your neutral, "ready" athletic stance. Look at the "backpedal guy" again, and notice that he uses a full range of motion, from deeply flexed to fully extended, as he absorbs those bumps. Any equipment issues that hinder that range only add challenge to bumps.
At your skiing level--which is, again, far beyond beginner!--if you have not had a good alignment specialist set up your boots, I would very much encourage you to do so. As you advance, the fit and setup become increasingly critical. You need all of your movements and range of motion to manage your skis--you can't afford to use any of them just to compensate for sub-optimal equipment setup. It will help with much more than just moguls!