Urgh.
Speaking just for myself, the whole "float above the substance" concept has never been satisfying to me, but, much like Democracy, I can't think of any better alternative.
However, if that's the ruling, then a ward against animals would not let a mage put their hand down a wolf's throat, either, or perhaps not even within the mouth. If the swamp is the faerie, then it could be argued that the swamp, as a whole, reacts to the ward, and not just "things" in the swamp. So, as soon as the ward is up, he can't interact with or penetrate the swamp in any way, shape of form, not even to enter it, any more than he could put his hand inside the wolf without technically touching it.
It's like being warded against a room - you can't even enter the room. To enter it and not be able to touch anything within it would be a different ward.
What if he's already there?... expelled, I'd imagine, or the ward would just fail, or, perhaps, he'd just be frozen in place, as the ward prevents any interaction. If you tried to ward yourself against the room you were sitting in, what would happen?
Now additionally, as a good SG, you don't want to give away too much, but you want to give the hints they need to solve the puzzle. If the mage can enter the swamp, but can't touch anything there, it will be clear that the swamp is "fae" - not necessarily "a" fae, but generally fae in nature. But if he can't even enter the swamp, and he knows he can approach other things that are fae, there is more information, an apparent paradox that might lead to the answer. (This is where you have to have players who are both 1) moderately intelligent, and 2) trusting that you aren't just screwing with them arbitrarily.)
If this requires changing history, and going back, then ~do~ it - better to apologize, and get it right, than be stuck with an unsatisfying patchwork of bad interpretations from here out.
Good luck.