Hardwood floors extremely buckled and raised, moisture or tenant damage?

[Matt W.]

I recently had a tenant move out. He claims that in a spare bedroom, which was hidden by a bed, when he moved the bed out he discovered an extremely raised section of the hardwood floors. The "peak" of the raised section is about 4" higher than the rest of the floor. It's right in the middle of the floor, not near a window or any water source.  None of the other planks are cupped or show signs of water damage. 

I don't see a water stain or pee stain on the floor.  It seems wild that it would buckle that much right in the middle of the floor. Maybe each board swelled and the pressure all came together in the center.  This guy has been a good tenant and I don't want to unjustly accuse him, but it seems weird. BTW the house is on a crawlspace, not encapsulated but not soaking wet either. 

Anybody had this happen to them?