I thought I was playing three-check so I played three-check opening.

I thought I was playing three check but I was not.

I often forget if im playing with increment in blitz or not. Its a good thing i dont play variants or else ill be suffering like that in every game

How is the game a draw?

He was probably playing against Stockfish and wanted to play three-check

Instead of what he was playing

You didn't play a 3 check opening. You squandered white's opening advantage of 2 points, then a further 3 points by your fourth move. Ie you lost the equivalent of a rook. It's an abomination of a 3 check "opening". After the first four and a half moves, it's never been played once in the history of 3 checks in the opening database.