haha I won?.....didn't play against you.
But it did happen also to me. during 4 seasons it happend 2 times that I had 80% and still lost the match.

Indeed not the strangest thing in-game.....
But as far as I can see, you did get that 80% because your opponent has 1 AMC and no ST, so your defence and midfield had almost all the possessions they can!

But agree, result is kind of strange!
Hope for you it won't happen much