Oooooo...Greg E. will have fun with this one, I'm sure.
So are they saying you only do double extension, as in only hips and knees? So how would one go from the "jumping" to the "landing" stance without extending their ankle? Ever tried jumping without extending the ankle? It's pretty tough...
There is a difference between *trying* to go up onto the toes and aggressively "jumping" upwards while having the heels leave the ground ever so slightly. If one's heels *ever* leave the ground by any miniscule amount, or for that matter, significantly unweight during a PC, I'd say that triple extension has occurred. Why purposely try to leave the peripheral muscles out of the movement? I'd venture to guess that the ankle extension is much less during a PC than a squat clean, but I don't see why it *shouldn't* happen.
I was just watching some hang power cleans on YouTube, by guys doing 350# plus. They all tended to land with severely wide stances, however, every one of them extended the ankle. FWIW.
Anyway, I'll let the forum-master have his say.