The assumption is that people used “grapes” in reference to the original tale. It’s very common for the general population to misuse or reinvent matters from popular culture. One very famous example is the line “Play it again, Sam,” which isn’t actually from Casablanca. Another one would be calling Dr. Frankenstein’s monster by his creator’s name (Kurt Vonnegut’s pet peeve). With that in mind, I think it’s a pretty solid connection.
As far as the whole onions/apples/fruit/genitalia thing, that goes back pretty far. In fact, I’m sure it even predates this erotic passage: “O Romeo, that she were, O that she were/an open-arse and thou a popp’rin’ pear.”
Are you suggesting that ‘How you like them apples?’ carries a sexual context? Plausible, especially a male taunting a male. Sort of a ‘How you like these balls?’
Interesting.
PS - You’re right that popular usages often varies from a literal meaning. My pet peeve is ‘The proof is in the pudding’.
That was actually in reference to what Kappa said. I don’t think “How do you like apples?” is sexual in nature, although apples can be sexual in other contexts.