Rear ender, run under, roll over, sitting duck, or at fault fatality crashes will end driving careers at most front line companies. Even the few who qualify as sociopathic need a paycheck and understand this. Reason enough to believe that this driver was doing nothing more than making sure he didn't grind you into the pavement.
Unfortunately drivers of big trucks do some not so smart things, as do we all. Except with trucks the results are magnafied because of the size and weight involved. It a good practice to give big trucks plenty of room and plenty of attention.
There is a book titled Driver, by Phillip Wilson which chronicles a refridgerated truck driver's first month or so as a trainee. Not a page turner, but lots of insight into the world of over the road trucking. These guys earn their money.