I'm not a judge, but to me cyclists riding two abreast do not impede the flow of traffic if the lane is too narrow for a bicycle and a motor vehicle to safely share. In other words, if the lane is narrow enough that the cyclist should be in a road position that a motorist would have to change lanes to pass, then it doesn't matter if it's a single cyclist, or two side by side.
However, in a lane wide enough to safely share that would not apply. On any road with more than two lanes, the motorist can pass in another same direction lane.