Happens more often than you'd like to believe. I assume that the front bit of the towbar is still stuck to the aircraft and the shear pins did their job and popped the bar off, only for the aircraft to run over the tug.
None of the airports I've worked at have had mandatory communication between tug and engineer/brake rider during towing so I doubt they were in communication either.
Hoping for a speedy recovery for the two tug guys