Earlier quoted context omitted.
If this was such common knowledge amongst his students at UCF, then why was this the first time that the professor saw the bimodal distribution in the test scores? Why didn't his Summer class's test scores have the same distribution? I think a lot of the comments in this thread are making assumptions about what the students did or didn't do, and might possibly be excusing some unethical behavior because of faulty ass…
As someone who works with data I can tell you that distributions can take on all kinds of unexpected shapes, especially when n=600. I think he's bluffing - the stats can't prove that anyone has cheated. That said, the deal he offered sounded pretty good when compared to the alternative.
I would love to hear some statistics folks weigh in on this. Or: speculation ftw!