I thought you played this game rather lethargically but although your opponent was lower rated he/she did play a decent game. Got the good bishop out of the opening and spotted the sac too so kudos to him/her.
The best 1200 shockers come from the jerks who have highest rating of 1600-1700+. As per usual, I go in and underestimate the opponenet as stated before and then proceed to have me arse handed to me....:'(
Another good example; this was a obvious draw against weaker opponent because I wasn't paying attention to locked pawn structure. When I realized it is a draw I was so frustrated I ripped the position open, sacrificing my two pawns. I calculated that he can win but I knew that his single mistake would cost him a game and I was counting with it.
Counting on your opponent mistake it is very lazy and bad habit which is almost always severely punished...
I still lose a lot easier to an 1350 than to an 1600. Weird at first glance, but it is not strange at all. I play at 30% of my strength against weaker opponents and I can't help myself 🙁