2 QxNd5 is clearly a mistake, but I can't see how in your puzzle, Black is better, let alone winning, after 2.Nc3 or 0-0 or even Bd2, all of which almost forcing ...c6 and then e5 could become weak.
A better first move is probably ...Be7, pressuring the knight and thus developing the bishop with tempo, unlike your solution which is a one-move trap.
I know.It is a trap for weak players. I wrote it into the comment section of the puzzle, but it doesnt seems to appear there.
Ok, sorry. But instead of a comment that does not appear before having fully solved the puzzle, I suggest you rate the move with a '??' which will appear when played (thus warning the solver it is not the best move).
Try moving the bishop first.