I'm saying that if you, a person who is probably not privy to the medical details of another random internet poster, cannot factually assert that dietary changes had nothing to do with his hay fever, then it is inappropriate to assert that it had nothing to do with his hay fever as fact.

We know that there are foods that have medical benefit. There are foods that contain anti-histamine capabilities, for example, or decongestant capabilities that could have been positively impactful on hay fever. These may have been a part of OP's dietary supplements.

Without knowing what the supplements were, we cannot dismiss that they might possibly have been of aid.