JASP, trying to watch this video closely to see what was going on the the funky transition thing was making me feel like Mr. Magoo,,, but at your question I've gone back and tried again. I think with my second effort I have it figured out now.
Yes, a form of diagonal stride skating, but not out of desire,intent or preferential habit. More a byproduct of an end of the turn balance issue. I mentioned to chanwmr in my first about the leaning in problem, and offered some drills to help fix it. If I'd made the effort then to look closer at the transition glitch instead of schluffing it off to younger eyes I would have made the connection between the transition problem and the leaning. They're completely related.
Because of the lean chanwmr is loosing his balance on the outside ski in the bottom of the turn. The outside ski thus tracks away from him and he falls on the inside ski which is a bit diverged to finish the turn. He follows that fall on his diverged inside ski, with a quick pull back of his departing outside ski,,, thus completing the perceived skate step.
chanwmr, have another look at your video and look for what I've explained above. There are a couple other drills you can do that can help this issue by forcing you to maintain your outside ski balance all the way through the turn. The Schlopy and the airplane wings drills will do much to resolve this, but you can also do "Inside/Insides" and "White Pass Leans".
The inside/inside drill has you balance exclusively on your outside ski, with your inside ski lifted, all the way through the turn, then when you touch that lifted ski back onto the snow during the transition between turns you step down onto it's inside edge and immediately begin the new turn. You can't fall off the outside ski prematurely and do this drill properly. If you've become accomplished with the airplane drill you shouldn't have much problem. The biggest challenge will be holding the inside ski consistently off the snow,,, but that's a good skill to have under your belt too. If you have a lot of trouble with that I have a full progression of drills that will get you there, but it's too detailed and comprehensive to explain in this format. Have a look at the link below this post.
The other drill, the White Pass Lean, is a step above inside/inside in difficulty,,, but it too guarantees you wont loose your outside ski. That's because the drill requires you to remain on your old outside ski all the way through the transition, then roll it over onto its outside edge of that same ski to begin the new turn. The other ski should be continuously held up off the snow as you do it. This forces you to begin the new turn on your inside ski, followed by a change to the outside ski when you reach the falline (put down the outside ski and lift the inside ski). This drill is very good because it actually requires you to actively untip your shoulders when you reach the falline and angulate over your outside foot/ski. It's a move you can really feel, and so makes you quite aware of your state of angulation at all times. Without the move, you can't make the switch from inside to outside foot.
I've put a video together in which I demo some of this balance stuff. Look for the White Pass lean at 4:36. You can see me make the lean to angulated change at the falline.
As I said, the White Pass Lean is a difficult drill because it requires you to start the turn on your inside ski. Inside ski skiing is a high level skill, but it's a valuable one worth working on. The link below provides a resource for doing that too.