Quercetin is present in grapes. Wikipedia says it's "the main flavonol" in both red and white wine ( https://en.wikipedia.org/wiki/Phenolic_content_in_wine ).

It is or at least was pretty common to hear about flavonols, flavonoids and specifically quercetin in various foods and their purpoted health benefits. Seems we've moved on to other compounds that are not yet known to be ineffective.