I don't know what I would do differently in your case, I would probably do the same thing that you do. I can understand not wanting to make a left turn from the road. Would the guy have been bent out of shape if you had continued straight instead of turning left onto the bike lane? I think you just came across one of the many people who are angry at the world and constantly look for "problems" they can "solve" (there's a German word that fits well, streitsüchtig, and I can't think of a good translation, but it describes people who enjoy being argumentative).