I'm not going to be too harsh on the truck driver. Mistakes happen. Plus, he was hauling two heavy trailers in tandem, which might've made it difficult to feel the extra weight. As for looking in his rear view, yeah, he should have. Had the truck driver done that he most likely would have seen the car hooked to his rear wheel. But then again, a lot of drivers don't constantly check their rear view mirror either.
Definitely the fault of the trucker but maybe he's got a good record and thus, deserves a chance.