Originally Posted by
exerda
Could be the pilot reported an "unruly passenger" or something to that effect, and the cops felt the need to investigate on landing.
I doubt it was pilot initiated as OP reported the pilot was "hopping mad" at being questioned by the police which wouldn't have been the case had he reported the passenger.
While the pilot was out of line with the poke calling it an assult seems an overreaction to me but that's just MHO.