I don't know what the source was, but I edited a forthcoming book that includes that tidbit, and I know that said book was meticulously fact-checked. A lot of dubious shit was spiked during the fact-checking process, but this particular piece wasn't.
The long and short of it is that when Disney first built the ride, the plastic skeletons that were available weren't remotely realistic, so they used the bones of cadavers from UCLA's medical school. Of course, fake-skeleton technology eventually advanced to a point where the real bones could be replaced, but actual human bones are still displayed in the captain's bedroom.
So anyway, yeah...Mayhem is merely following in the ghoulish footsteps of one Walt Disney. Nothing more kvlt than that.