Mysterious blunder

I played this game perfectly, but Stockfish doesn't understand some moves.

1. ... f6
Not the best move, but it's part of the opening.
2. ... Kf7
Again, part of the opening.
55. ... h3
Can someone explain how is this a blunder?

Stockfish is a computer, not a human. It always calculates the faster way to checkmate, and the faster way was 55... Kf4. Don't think about it that much, 55... h3 still wins.
Do you want me to explain f6 and Kf7, or would you prefer to figure it out yourself?

Actually, three moves lead to fastest checkmate and it's far from 52 moves.
55. ... h3 -> mate in 10
55. ... Kf3 -> mate in 10
55. ... Kf4 -> mate in 10

Some openings contain questionable moves, that's normal.