I was going to say this too, but I didn't want to assume any feelings on your side or imply something that you didn't already feel.

I would really really be upset, because I, too, would think that he was staying because he wanted to... but then, devil's advocate here: he probably WAS staying because he wanted to, but he also has to be ethical. Which means reporting that he stayed longer and provided support. Know what I mean? He wanted to but also has to be ethical. If he didn't want to, he wouldn't have done it.

I don't think that you are going to sound rude bringing this up. I think your reaction is entirely normal and expected.