Did...did a monster from ancient folklore have a better grasp of consent than many modern humans?"
Well, no shit. Folkloric creatures know that rudeness can get them fucking killed in nasty ways, and ain't about to take the risks.
All of our old supernatural creature stories are thinly disguised guidelines for teaching kids about life. We tell them to stay on the path not because some witch out there is waiting to grind their asses into gingerbread, but because out in the sticks with no artificial lights, one storm pops up and you stray off the path and get lost, exposure can and will kill you.
Warnings to be on your best behavior among the faeries are warnings to mind your manners among strangers.
Faeries = Fae = Foe = Foreigner.
Manners were designed to let us talk to people different than us without bloodshed, which was easy to do if you didn't know the rules. So you got as polite as possible and hoped it was enough.
Modern humans (or at least first world suburbanites) have no fucking concept of rudeness getting your ass kicked or even killed, and haven't for decades.
There are cultures that have that concept thoroughly ingrained, but these days they get laughed at or chided by first world suburbanites for expressing it.
When I was in Iraq, I'd gotten some renfaire pics in a care package, and another guy in the unit expressed some rather enthusiastic approval of how Merry looked in a bodice.
When I mentioned matter-of-factly how I couldn't see that, what with being her brother and all, he immediately jumped back a good ten feet, hands in the air like he was being held at gunpoint, and let loose a stream of apologies as fast as he could speak. It took a good two minuites to calm him down.
Where he was from, speaking in such ways about someone's sister resulted in an ass kicking if not a knife. And this was not only understood, but widely approved of throughout the neighborhood.
Me, a first world suburbanite raised in the Rennie community, shrugged it off.
Going back to vampires, they're generally considered a metaphor for lustful behaviors. Which means the warning in the original post is that even though he's minding his manners, the intentions are still blatantly less than honorable. (which predates the nice guy movement by at least a century, now that I think about it.)