No, I didn't mean that I cheat, and therefore everyone else cheats. I meant that the one time he got to see what's going on, he found that nearly everyone cheats. Unless he has some evidence to the contrary, a reasonable conclusion is that cheating is near-universal.
Evidence to the contrary could be, for example, that this class was very different from a typical class in some way, etc.
Evidence to the contrary could be, for example, that this class was very different from a typical class in some way, etc.