I don’t believe people would share bad private reviews and positive public reviews.
I believe there’s something else.
Fiverr would warn you first if it was a simple violation. But the fact that they banned him means a lot of people said his work was not ok. And I do believe multiple people went to customer support at the same time. They won’t disable people randomly…
Did you have multiple 1-2-3-4 star reviews recently? Or only that kind of review?