It's actually thanks to buggy nodes that the monsters fail to attack you. Rebuilding the nodes with a non-bogus nodebuilder breaks the effect. Ports that always unconditionally rebuild nodes also break the effect. Still, it's a pretty amusing effect, for a whole half-minute.
When a map only has one sector, the monsters won't wake up from seeing the player and won't attack either, that's something I learned from testing custom monsters, but I'm not sure of why it happens.
My only guess is that there's probably some function that checks if a monster can see the player by comparing the heights of sectors or something like that, and since it cannot compare two sectors when there's only one it never gets called. That's only a guess, I really have no idea, I couldn't find anything when I googled it.
This could ascend to Cacoward quality with a simple copy/paste clone job -- then it'd be Double Impact. *booed off stage*
It's an adequate "my first map." You chew up lumps of fodder with weaker weapons in small rooms with sharp directional lighting for about 2 minutes. One of the secrets was cool. Satisfying enough.