Yeah, those are exactly the differences.

It's very easy to argue speeding is immoral: it's immoral to disobey any law or regulation passed by a democratically elected government if these is no other conflicting moral principle. So you can speed to rush to a hospital, for example, but everyday speeding is immoral both because it breaks the morally legitimate democratic law and increases the chance of physical harm.

For many people, cheating on a test is little different from speeding. Calling it "self-harm" is a stretch, and there's zero direct harm to your classmates if it's not graded on a curve (which I haven't seen in a long time). And you could easily argue that the marginal difference it makes to the value of everyone's degree from that institution overall is basically as negligible as the marginal difference it makes to public safety as speeding by 5 mph does.

Also, different exams are different. Fewer people will be bothered by cheating on a freshman year calculus exam, whereas cheating on a final qualification to become any type of emergency responder is far, far more serious because somebody could directly die as a result of your lack of knowledge.