I wouldn't get too concerned about someone who doesn't acknowledge you especially if there is a lot of debris on the road or rough surface, or a lot of traffic. etc.the guy just may have been concentrating on things like that or cadence or who knows what? not a big deal. the thing that bothers me are people who have this blank stare and weird facial expression that are almost looking right at you and they just blow off your wave or "hey how ya doing" and say nothing. that's really weird. but to each his/her own I would'nt let it ruin your day.