How about a boat distress rocket? (Probably a lot closer in than you believe it is.)
I did think about that and there are two large lakes (Falls Lake and Kerr Lake) and a few more smaller lakes but these appeared to be well beyond. But the red glow does lend to the idea of flares though the altitude They reached was extremely high for a flare. Also, I noted at the time, a couple of airliners that passed by at a much closer distance but not close enough to see the red and green nav lights