No, this is highly plausible. He took the wrong exit, and got stuck on an international bridge. He was told he would have to cross into mexico in order to turn around. He didn't have a choice.
I would've set the parking brake, got out of the truck and walked back to the US side of the bridge before entering Mexico with a load of anything not intended to go there. Let the "authorities" figure out what to do with it. It's not my problem that they don't have a turnaround.