I do not see it as being so implausible that he got mixed up due to being sick and thought he was doing one thing while he was actually doing another; as you said, among other things, he should probably reflect on how he takes notes.

I think that my overall point stands that there is not a good reason not to at least tentatively give him the benefit of the doubt that he screwed up in the way that he said that he screwed up, rather than assuming that he is lying and actually did something significantly worse, especially given that he fully admits to having screwed up and took full responsibility for it.