Denny may be on to something. BWOs are a bit out of season, is it possible the flies were actually calibeatis?

I think they have a very active swimming nymph that can hold the fish's attention...

pheasant tail. Chances are the fish didn't run away from hatching bwos, so if they weren't hitting the top they were likely gorging on active nymphs. The rs2 was also a good choice but maybe get it...