Car drivers often don't see bikes right next to them at all. They are looking for other cars, and can literally look right at you and not "notice" you. I think if you are over to the right enough to have a car pull alongside and share the same lane, then for safety sake you should assume they might go left, straight, OR right (in front of you) when the light changes.
There are other options I've read about and use myself, that might be safer:
If you're staying close to the curb, stop a little ways before the intersection, so that you will wait at the light between the first and second cars rather than right next to the first car. That way you can turn and get eye contact with the driver behind you while you wait at the light, and also let the first car go first for a few seconds so you can see where they are headed and not get cut off unexpectedly. Or,
Don't hug the right side of the lane at all when you get to the intersection. Get right in the middle of your lane and be a Real Vehicle so they can't sneak up alongside you even if they wanted, and signal the cars all around you boldly. You are much more visible to the cars directly behind you and in front of you, and less likely to get hit by them. You are partially invisible to cars beside you or if you are in their blind spots.
Needless to say, if you are going to go left at an intersection you should never be on the right side of your lane (I realize you did NOT do this).
Just some options to consider adding to one's arsenal of traffic moves.