"I always assumed that was the case and thought that the misunderstanding was fairly explicit in the lyrics."

Of course, there seem to be so many different versions floating around that it's hard to say if we're talking about the same lyrics - but I don't see that it's "explicit" in the versions that have her saying that she was "slighted" when he was toasting the ladies, and then give no further comment on that bit of business. Seems to me that's wide open to all kinds of interpretation ... No doubt I'm quite thick-headed, but I find the interpretation in question, whether on the part of my student or yourself, to be rather subtle.