You're 100% right, but most teachers teach more than one course. When I was teaching High School, I usually had three classes full of dunces like this, and then two Honors classes. So I'd have had to be a Delta Force ninja to teach three of my classes, and an erudite academic to teach the other two. Same teacher, different parts of the day.
Of course! I was simply allowing myself a snarky comment.
Regards,