Someone trying to get the pan off without getting all the bolts out is all I can think of. May have been swapped off of another engine that this happened too. Who knows. The story behind the engine history seems a little shady on the part of the seller......
Agreed that the back story is shady, I'm not really pleased
The flange of the pan was bent over the nut (it's a nut there not a bolt) and I had to bend it back to access the nut for removal, the damage was definitely due to an impact of some kind. I'm 90% sure it was dropped