Game analysis and accuracy

So in my most recent game I played black and made a pawn move that made the evaluation drop from mate in 3 for black to like -7. The analysis says this is a "missed win". I really don't agree here. From my understanding a "missed win" should be when the move changes the outcome of the game by best play e.g. a winning position is turned into a draw. I don't think that it should affect the accuracy either, I don't care if I my position is winning at mate in 3 or -7.

I have that one "missed win" in that recent game and no oher mistakes/inaccuracies and the analysis gives me an accuracy of 89.3, that's complete nonsense. How am I playing a "0 wrong moves game" without getting anything close to 100% accuracy?