Yes, that is 100% true, but that doesn't discount that there are only two turns.
The physics of a ski on 2d snow is really simple for the most part. There are plenty of websites like this that explain it:
A carved turn only has two forces applied to it, a tipping force to the side, and a forward force to maintain tip pressure.
Any other turn requires a third force, a rotating force. Newtons first law demands it. Once the ski is broken out of a carve it needs a rotary force to change directions, otherwise you would go in a straight linee.
You can call either of these turns anything you want, but due to the force vectors there is only two of them possible.
I lifted my skis, stemmed, and did all sorts of aweful skiing tonight. No one of it in the name of good skiing. I don't think I have skied in such nasty conditions.
Where is that rotary force coming from?
It could come from femur or it could come from the ground reaction forces (GRF). Generally the more of the forces that come from GRF the better the skiing.
Do you know that it is not possible to provide a continuous torque from the femur to affect the ski? By Newtons third law if you twist the skis you twist the upper body the other way.
Most people who think they are steering by twisting the femurs are not, at least not in the way they think. You can get some temporary change of the force but that is by twisting the upper body the other way. I'd rather call that countering.
You could argue that a carved turn is when the platform angle is larger than 90 degrees. I'd rather call this an edge locked carve. However, not even this definition would be strict because in reality you have torsion along the ski so that tip and tail has a smaller platform angle. There is no finite point where the whole ski becomes carved. What is carving then?
Further in reality the platform angle changes rapidly all the time due to terrain.
I used to have the opinion that a carved turn needed to be edge locked, but due to the above and after reading BTSs motivations in another thread (a long time ago) I changed my mind. I agree with the definition that FOM and BTS have in this thread. It is much more useful.