Its is not a blunder in my opinion - analysis says it is.

Hi,
i was struck after an analysis (yes i know not to analyze blitz and less TC but just wanted to see the tactics :))

After ply 52. .. Kd7 (black king d7) engine pointed its a blunder... but its not - the mate looks forced and the other only choice which is Kc7 results in the same #2...

Is anybody aware of this issue? Are there other known examples of this type of categorization or other examples?

Is thre an explanation or reason of the depth of calculation? Is engine counting and analysing from the end of a game?

Although basically no one would blunder this position, I'll bet that the best move gives more chances for white to blunder than Kd7, which is why it's considered a blunder. Also, when I looked at the analysis, I didn't see it as a blunder but I could be mistaken.