The tub and bumper move independently since the tub is rubber mounted. Things can twist and flex - especially while offroad if there isn't proper clearance. I don't know if it would be enough pressure to cause the damage the OP has but it's possible.

I too am curious what their verdict was.

 

I also have a 2014 JKU and I'm running into the exact same issue. I'm running Rockhard bumpers front and rear, I love them. I can see though where it looks like the tub and the bumper bade contact on the drivers side. There is clearance between the bumper and tub and all bumper hardware is tight so there has been no movement of the bumper on the frame. I'm not sure what created the issue, but I'm taking it in this week...