If the parking brake had been set during push, its likely the sheer pin would have sheered and the tug would not have been able to tow it back to stand without a new bar.
Agree, when they are pushing the airplane
straight rearwards, but in this particular case they were just
turning the airplane, with the bar almost at 90 degrees to the fuselage, so maybe the pin didn't sheer despite the violent stop. The airplane was shaken above all
laterally.
Btw, just speculating...
Must have been really embarrassing for the Captain
