I've seen some bikers who run red lights/stop signs, pick and choose whether to act as a road vehicle or a pedestrian, ride the wrong way, cut in and out of traffic by cars' blind spots... I've also seen bicyclists who don't use headlights/rear lights and reflective gear which makes it impossible to see them in the mornings or evenings. if he is one of those I would be worried.
But at the same time there are drivers in this area who are INSANE. So it could be that too.
This article is useful (and a bit funny). How to avoid being hit by cars:
http://bicyclesafe.com/