He clearly didn't mean it in a sexual context. Your sarcasm and cynicism is detestable.

It was in reply to the comment "Impressing girl X strong enough to kiss you [...]", which would suggest he did.

Still, if persistence to get a "yes" is to be equated with rape, then this ought to be really offensive to all rape victims out there because it totally trivializes the crimes perpetrated against them.

"No means no" means everyone has a right to control bodily contact. It does not make asking a girl out for coffee the 100th time and getting shot down the equivalent of rape. It does not mean taking that as "try harder" (however stupid that may seem to be in context) to be the equivalent of rape. It is only when non-consented bodily contact is at issue that any equivalence can be drawn.

I agree that blanket rules are dumb. However The OP's original advice is dangerous because those who don't know any better could misinterpret what he is saying. It's better to start from the default safe postition of "no means no" and work backwards rather than listening to random strangers of the internet who tell you otherwise.

But that's violating a very specific line and you can't generalize out.

"No means no" means "everyone gets a veto power over actual contact." That's all it means. it means you can't say "mixed signals mean yes." All it means is that the specific line, over contact, is one where people retain a (legal as well as social) veto power over.

Does that in itself prove the point wrong?

Not necessarily, but it should definitely make him question whether his phrasing/thought was the most pertinent reaction he could come up with.

You realize that what he is arguing is more like "do you want to have sex?" "no" time passes "do you want to have sex?" "yes" sex then "do you want to have sex?" "no" sex.