It has been pointed out…these were former students of the prof in question.
Is it skeevy? Probably. Is it abusive? Meh. At what point in time is a student former enough to date? A week? A year? A decade?
I know people who were colleagues, with one in a non-direct supervisory executive role. He left the company before they started dating so that they could start dating. They’ve now been married for 20+ years.
Once the power imbalance has been eliminated, I don’t see the problem. We’re not talking Stockholm Syndrome, here.