My question is, who come up with idea of piloting a vessel inside building (mines in this case)? And how? And why? :p Is there any interesting story about this or there is nothing really to talk about, like, it just happend?
There wasnt any similar theme in any other game or movie before (or maybe there was??), so you were kinda first in this matter. It may be something from sci-fi books tho, like P.K.dike or Stanislaw Lem ones.

I know it maybe inappropriate place for this question, cause real developer of descent was parallax software, but since parallax is no more, and volition inc. doesnt have its forum, and outrage games is no more, this place is as good as any

My guess is someone who wanted something different than just the 2D games that were around at that time. ""For where your treasure is, there your heart will be also." -Luke 12:34

Descent was a singularly unique creation by Parallax Software. (follow and read those two links).

It was really kind of a snubbing at then very popular 2d Doom and every incarnation of FPS that it spawned. Descent was the ONLY 360DoF game. And pretty much remains so. And if you mention Forsaken as an equivelent, I'll hunt you down and kick your cat... it really wasn't and it was a very bad game. (imo)

Books came later and were pretty good. There was never a movie made, but one had been planned.

and that's about it in a nutshell.

His name was Matt Toschlog.

yes, that's what the wiki link points out.

There are quite a few interviews with both Matt and Mike.

You can find them here: http://www.descent4.org/interviews