Is it possible to have a 0/0/0 game and lose in an OTB game?

You’re right.

A 0/0/0 where half a centipawn loss is considered a mistake would be pretty impressive in most cases though!

I've had one my OTB games analyzed aby lichess engine and got 0/0/0. Just un eventfull game with no truly difficult choises. Threshold is huge (half pawn) which makes 0/0/0 reachable for noobs given that you trade most of pieces away soon in forces way

Its enirely possible. Even if all your moves are recommended by Stockfisch with max depth, defeat is not impossible.
However, how does Stockfisch evaluate its own losses?