Actually I've never seen the animated series and I don't think I've read the story, though it's possible - I just wrote myself into a corner.
What happened was that I described the hotel before I realised that Lex was going to be there - DeMarco (who was a one-episode villain in Angel with a line in magical mind control) was originally going to be the main bad guy, not just a flunky, but it didn't work when I tried to write it. I needed a big bad: in the Buffyverse vampires are usually the big bad.
Once I'd realised that Lex was a logical choice to be the vampire, I knew that there would have to be kryptonite. And once I knew that, I needed a way to save Clark. And since I'd already described a hotel with lead-lined walls and radiation-proof windows it wasn't very difficult to come up with an answer...
Later edit - forgot to say that the special vampire-friendly Necro-Tempered glass is also from Angel; Lexcorp does seem a logical company to make it.
Another late edit - Back when I was ten or so and reading Superman comics in the early sixties I recall him having some Kryptonite-proof clothing he used in the laboratory in the Fortress of Solitude. I'd forgotten it when I wrote this chapter and wrote my earlier reply, but it was probably in the back of my mind.
