It really sucks when this happens but it's easy to avoid a mouse slip.

Wikipedia - Glossary of chess

This interesting website has about 75 pages of "commonly used terms in chess".

mouse slip - A fumble by a player in the use of a computer control tool while playing chess on the Internet, that results in an unintended move.

castling A move in which the king and a rook are moved at the same time. It moves the king from the center to a flank where it usually is safer, and it develops the rook. It is the only time two pieces are moved in a turn. Castling can be done on either the kingside (notated 0-0) or the queenside (0-0-0). Castling cannot be done in reply to a check, nor if the king were to cross or land on a square which is under attack by the opponent, nor if either the king or the rook involved has already moved.

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I recently won a chess game because I had an advantage when my opponent was trying to castle his King and he fucked it up with a mouse slip.

At https://lichess.org where I play chess, when I move a piece I can use my mouse to slide it to move it, but that's usually a bad idea. To avoid mouse slips I can click on the square where the piece is and then click on the square where I want to move it to. I almost always do this thing and I never have mouse slips.

This is the chess game. I had the White pieces:

https://lichess.org/nlejijqe/white#0