I don't know if the OP forgot to unzip the zipper, if OP didn't think they needed to open the zipper or left it zipped on purpose
Was the CM within reason to unzip the wallet, yes
Should he/she have asked first: yes (even though all bags are subject to search, he should have asked the owner to unzip it, which is usually what happens)
Could the CM have been tired of asking, going through the motions of bag check and just didn't think it was important to ask: probably.
I don't use purses and very rarely do I take a backpack to the parks. I actually use a regular "man's" wallet. I take the single key of the car and put it inside the zipper inside the wallet that is meant to hold spare change. I have never, been asked to open that zipper, or have security ever touched the wallet when I go through the metal detectors. (since I don't have the bag I can bypass the bag check) If they felt it, I'm sure they would ask me to open it. And that's the problem I have with the current "security" checks at Disney.