Saliva contains a mix of what are called proline-rich proteins (PRPs). They are interesting molecules that should adsorb bee venom, although I don't think anybody has ever looked specifically for this. At least when I ride hard, my mouth dries out which would increase the concentration of these PRPs, so intense riding could be a factor in reducing the reaction.

OP, next time you might want to also get some aspirin, grind it up and put it on the site of the sting. Aspirin also adsorbs the venom and reduces the reaction. Yes, I've been a bee keeper for many years and have had my fair share of "gifts". Charcoal also works, but I wouldn't recommend that when the sting is in the mouth.