Ghost shifting sometimes happens when you push particularly hard on the pedals and cause the bike frame to flex some - particularly if the derailleur is already a bit out of adjustment (which a bent hanger could cause). I agree with Rowan that a heavy load either on the bike or trailer wouldn't cause a bent hanger - usually that's the result of laying the bike down on that side, leaning it against something when parking, or from a stick or other object knocked against it while riding.