"Miraculous Moop" Card (Moop's Monster Mashup)

[josh_dog2]

The card states "The munchkins must be losing by at least 10 points at the moment you play Miraculous Moop. The munchkins automatically win that fight. This cannot give a munchkin the winning level. Usable once only."

Tonight we were playing and a player was at level 9. Played a monster, then a wondering monster plus another monster. At that point he was way beyond losing by 10 and played this card.

I argued the card cannot be played at all because he would get the winning levels. Therefore he would have to deal with the monsters in a different way. He argued the card could be played but that the levels would just not count and he would remain at level 9, while taking all of the treasures.

Could someone provide some clarification to the wording of this card?