I wasn't there, as it happened to my buddy, but I think it's quite obvious he was waiting for my friend to slip up and make some dumb infraction so he could write him a ticket.

And sure,t he ticket may be a valid complaint under different cincumstances, but in this case he was on a road all alone. The purpose of a turn signal is to let other people driving along the road know you are turning or making a lane change, so they can adjust thier trajectory as such. If there's no one else there, what's the point of the signal?