Strange Bump on Side of Driver's Seat
 

I'm posting this for a friend/coworker with a 2012 CLS63. He recently noticed this bump on the side of the driver's seat that he hadn't noticed before despite owning the car for years. I'm guessing it's related to his inflatable seat (passenger side doesn't have it), but he doesn't think it has always been so noticeable.

Are any of you familiar with this? Thanks.

https://cimg7.ibsrv.net/gimg/www.mbw...7ec70e6dad.jpg