Your findings are right in line with what I’ve read about deer’s preference in acorns. Burr oaks are white oaks, and they prefer them because they taste better due to less tannin to begin with. The red oak acorns have more tannin, which gives them a bitter taste. They’ll eat them, but typically after they’ve sat long enough to lose most of that tannin. Or maybe they just deal with it after the white oak acorns are gone. I forget, exactly, but it’s something along those lines.