My opponent made two blunders in the opening and resigned at 11th move. The two blunders have nothing to do with his unfamiliarity of sveshnikov variation of the sicilian defense, but I did have big enough attack because of it. Go through the game to see more details.

Below the game is the continuation in a form of a puzzle - try to find the checkmate!

Isnt Rb1 mate as well?

 Yes, it is the arabian mate at 90° angle :)

The board doesn't let you put particular sideline as one of the correct answers, so I chose more interesting mate for the puzzle.

The decisive error was castling to the weak queenside. Was it not?

Black had 4 pieces aimed at the queen side with only 1 defender for white and the dark squares were weak.

I wrote the exactly same thing in the comments of the game. White's dark bishop was also stucked on the other side of the board, so yes, his only defender was queen. I wrote in the comments of the puzzle what happens if white defends with the queen.

Very nbice mate. I struggled to find 13 Bc1, was fixated on Nxa2, lol

It may be hard to find without calculating every white's option. The idea behind 13...Bc1 is of course that if white plays 14.Qxc3 (preventing mate on h7), black plays 14...Qxc3+ and will checkmate with 15...Qb2#.

13...Bc1 also makes arabian mate available because after 15...Rb1# white's rook can't capture on b1.