The more interesting tidbit is that this is actually pretty common. The prop house using real skeletons was actually pretty common and not unique to this production. The notable thing about this film was the sheer number of skeletons that they used, so they basically scooped up everything that was out there, and how much the live actors actually interacted with the skeletons. It wasn't particularly unusual for skeletons to be used as props.

Really, just about any time you saw a skeleton on screen before the 90s or so, it was probably real. A lot of real world props and decorations also used real skeletons, sometimes to the surprise of the people using them. For example, if you rode the original Pirates of the Caribbean ride at Disney Land, you saw real human skeletons.