Toi, that’s right. It looks like it has to do with it being considered the same split second rather than a sign of what his real Daas is.
It’s interesting that the obvious Chiluk is not mentioned. In the case of Kriah and a mistaken Hafara, there is no action against the true and final intention, whereas in Kedushin and Geirushin he wants to undo what he just did. However, it seems that the reason the Rishonim don’t say that is because that would have large ramifications that aren’t necessarily true.