I'd have thought that both bikes would be stopped by the same thing in Mud. The front wheel getting bogged down and slowing both down. Normally the MotoX would be moving quicker so get further before getting stuck as well as easier to get going again.
You've got to remember that a MotoX will go up virtually anything you throw at it. I've done stuff that I would never try in a 4X4. It usually involved lots of effort to get the bike over the top with the bike in mid air.
Ed