Maybe the hitch was an after-market hitch, added on after the original purchase.
Original equipment
For the OP: Did your brother purchase the Motor Home brand new or used? If used, it's possible the previous owner had the hitch installed. And rather than welding, used the bolt-on method.
Bought it used but this hitch is original equipment
If this is the case, it's possible the frame was never intended to support a hitch capable of towing anything.
This Thor Product with the original tow hitch is rated well above the weight of the toad.
My previous trailer (Thor product) had a receiver hitch on the back, clearly labeled with a weight limit and clearly labeled not for towing.
This is not a trailer or with wheel which I would not tow with nor recommend towing with
My current 5er came with a factory installed hitch (welded) and it si clearly labeled with a weight limit and clearly labeled, Not For Towing. So, just wonder if the hitch was an after market?
I would expect Thor Industries to have welded components. I've never seen one that was not.
Me too, but Brother says he found this same problem occurred on a similar Thor product back in 2015. not welded then too... Welding is more expensive until hindsight is applied. LOL