Probably because he's totally lost.
Why resignation?
Still why? Promoting - then he could beat my Queen with his bishop. Mate with Rook, then he could threaten my Rook, with his King...Is there checkmate in #2, #3 or #4 ?
I dont handle so good the marks a,b,c,d,e,f,g,h and 1,2,3,4,5,6,7,8 and allways wonder what the heck those who use them are talking about. But I try (not reading from anywhere): white c2c1->Q then black Bfxc1. If white Re2e1+ then black Kf2. You cant do chessmate with only Rook, so it is useless to mate with only Rook...
Yes
Even it is so, that the more low rating player is leading, the possibility to stalemate is bigger.
A friend of mine who is about 1600 FIDE once lost his queen for a bishop due to a pin in a 90/30 OTB game against a similar rated player. He continued playing though, and several moves later his opponent's K and Q fell on a knight fork, so he ended a piece up and finally won the game (and no, I'm not talking about Josh Waitzkin in that movie). Crazy thing indeed.
Garry kasparov himself allowed a stalemate in a blitz game. Video is on YouTube somewhere. The look on his face is priceless lol.
Who? Is trolling? Me? No! I have to really carefully count especially alphabets before I know what square others are talking about. I can't do it in my mind. I have to see the board. And if there is not 1,2,3,4,5,6,7,8 and a,b,c,d,e,f,g,h marks in the borders I have to count for example "f"? Ok, it is a,b,c,d,e,f - it is sixth column...I can't do it backwards h,g,f,e,d,c,b,a so that it would be easier recognize: it is thrid from the right side. And then, when the board is upside down I get totally confused.

I was much dissapointed
even little angry
because my opponent made resignation in this situation. I think the opening and midle game was ended and the most interesting end game starting. Time was left over 15 mins in 30 min match. Maybe he got something other to do? Yes, my black c pawn was nearly promoting to be queen, but still :(