While you might think this is aggressive driving on the part of the cop (passive-aggressive driving, more specifically), a lot of cops do this to bring the speed down on a highway when everyone is driving over the limit.
I don't know if this was the case here, but one time I was racing down the Garden State Parkway, trying to get to the Ferry before a snow storm over took the road and two cops actually got in front of everyone and slowed everyone down.
While it pissed me off, they probably prevented a lot of people from spinning off the road or getting into accidents.
The driver with the dash cam passed on the right and could have and should have been given a ticket.
When a cop gets in front of you like that, you've got two choices: deal with it or pull over and let traffic pass.