Driving in the left lane is illegal in most places, so he was probably still breaking the law(unless on a call or in pursuit).
The left lane is for passing and moving over for breakdowns, police stops, and mergers. It irritates the heck out of me that so many "drivers" are ignorant to this. It is also extremely bad etiquette. It does not fly in Missouri, as we have strict enforcement of that particular law...especially in KC. Nebraskans are the worst; driving 60 in the passing lane in a 70 zone. Every darn day.
http://www.usatoday.com/news/nation/story/2012-04-19/delaware-highway-traffic/54409762/1