Actually a check is announcing a NON BET.
and I think allowing him to fold is absolutly correct when facing a raise. On the other hand, Allowing him to raise is wrong for the same reason, he's already expressed an interest in not putting money in play. Dunno how you guys play, but at our game, verbal declarations are binding. And he CLEARLY DECLARED A NON BET. Now if you really wanted to be a nit about it, you could say he wouldn't even be allowed to call. just so he wouldn't be able to profit from this angle shot.
After all, he's already declared a NON BET.