All I'm asking for is for some kind of confirmation that he thought the kids were actually trying hard, which we all know (without documentation, yes) isn't universally true of students.

It's also often true that instructors don't know what's going on in all the students' personal lives. People who are pressed in other ways don't always make it known, so you could easily see how you might mistake someone who didn't learn it with someone who couldn't learn it.