Why did my opponent resign?

Hi! 

I recently joined the 21st Chess.com Tournament (1201-1400), and in terms of rating, I was only 5th out of the 6 players that joined (including me) in round 1. 

2 of my games I won on time because the opponent never placed a move, but the rest of the games were all a challenge. 

This is one of my games against a 1400ish player, who I lost to during our 1st match but won against on the second. This is our second match: 

Yes, both of us had a few blunders, but it was a fun game! :)

Anyway, at the end-ish of round 1, I was second place in my group, and the last match of our group was between me and the 1st place player in my group (who was a higher rated player than me also!). 

I had lost against him during our first match because of a very stupid blunder where I just practically gave away my knight for free. 

For the second game (the last game of round 1 in our group), I made a stupid blunder AGAIN and gave away my knight for free.

I almost resigned then, but I played on, as this was the last match anyway. Also, I calculated that if (with the slighest chance) I beat this player at 1st place, I would tie him (with equal tie break points) at first and join round 2!

Well, in the middle of the game, and I was still down a knight. But then, the opponent suddenly RESIGNED! There must be a reason, (or is there a reason?) whay he resigned, but I can't figure it out. Can any of you guys help me? This is the game: 

Anyway, right now, I'm waiting for the rest of the groups in round 1 to finish their games. Our group is finished with Gubin and I tied for 1st (pretty rare thing to happen), with a score of 7 points each and 27 tie breaks. Here's the image:

Thanks for reading my blog post. I'm still wondering about the sudden resignation, so I wish somebody can help me out. :p 

Wish me luck! 

-Jae