When you were talking about the generation schedule I'm guessing that that the bigmouth buffalo you caught was not in the the park. Being that buffalo are members of the sucker family it wouldn't surprise that they would take midge larva. Food habit studies of smallmouth and bigmouth buffalo in TVA reservoirs have shown that insect larva are included in their diets.
Personally I've caught white suckers and redhorse while drifting nymphs. I wouldn't be surprised at all if they would take a size 22 gray nymph.