maybe he was going to make a left turn down the road and history tells him that unless you get in the left way back, people wont let you in.
I know on the beltway in the morning using a turn signal is an indication that there is space next to you for someone to hurry up and fill before you can make your lane change.
Maybe he should have waited for those of us that had the green light and right of way to pass by first and then pull out once there was a red light, thus giving him a break in traffic.