Even more so in the Dean Koontz stories.

David Bowie and Muppets don’t really mean anything to me, and I can rarely tolerate a musical.

I’m pretty sure they were being sarcastic. I’ve definitely heard of the movie. I just haven’t seen it (and won’t since it’s apparently a musical).

Since everyone in the comments seems to know, what’s this a reference to?

Y-level. Before 1.18 the top layer containing bedrock (ETA: in the overworld) was y=4.