Ah, I'm glad it's not just me that noticed - actually, in that video, there were a number of incidents that they missed - like use of 101 Dalmations animation in The Jungle Book (3 wolf cubs peering over a stone, 3 dalmation puppies peering over the arm of a chair...). Apart from the Beauty and the Best/Sleeping Beauty one (and I'm not entirely sure the animation was re-used there, there are just only so many ways that you can animate repetitive ballroom dancing), many of those films were from around the same time (Aristocats, Jungle Book, 101 Dalmations, Sword in the Stone, Robin Hood) so it was probably just a phase!