Looks like the event procs the first time you enter that room - it appears to be possible to navigate around that room without ever actually going into it.
I didn't program that quest and haven't played it myself, which puts me pretty far behind on figuring out what the limits and intended path are.
Which means I'll have to play my way there from scratch and figure out what's supposed to be going on.... sigh
Edit: Wait, I can interrogate the author about it... Oh Fr0sty....