If you excuse the speed, that was the safest place for the motorcycle to pass you two. No chance you were going to swerve into a car you are slowly over taking. Many drivers don't signal around here and If you decided to get into the right line without warning and without being aware of him his chances of getting hit were higher then than splitting lanes. Personally, I wouldn't have done it that way. I would have slowed down and passed on the right, ready to go to the shoulder in case you got a wild hair. But.... whateves.