Playing cards in response to a "Discard All" curse?

This is hopefully a quick and simple question:

Deck: Adventure Time

Battle was underway with me and partner A ready to defeat the door monster. I played a "Curse! Razzamafoo!" card on player B as I had a suspicion that he was about to interfere with the battle before it was over.

This card forces the player to discard their entire hand.

In response, he PLAYED his entire hand on our battle, raising the monster level to ridiculous amount. He claimed that he was playing those cards in response to the curse card I played, which everyone else at the table disagreed with.

The claim was that if I had played that curse on him outside of combat, he couldn't play the monster cards in response, but as it was in combat, he could. This seems like the incorrect way to resolve that card in my view.

However, with him being the only one with real Munchkin experience and the rest of us trying to get the hang of the game, we ended up leaving it at that and we had to run away from combat instead.

Seems to me that he could have played a counter-curse card in response, but not play cards into combat in response to a curse card that forced him to discard his entire hand.

Thanks for any clarification.

Playing cards in response to a "Discard All" curse?