Hades, as Emet-Selch in a sundered world, developed and perfected skills in getting what he wants out of people. He can make himself perfectly charming, someone you'd throw everything away to follow, someone loved. Of course he's just as capable of being someone feared and despised as well. It is not a new talent of his, but perhaps not quite as expected by those who knew him in ancient times.

In Duplicity he sees merit in making alliances with people and so he's cordial enough to the interesting ones. He might have been flirting, who's to say? He's eaten some food too and people like to be flirted with. It wouldn't have meant anything either way. Which is why he's completely surprised to feel Hythlodaeus from behind him, telling him they ought to leave before they're late.

"Late for wh— Excuse us." He tells his present company politely but confusedly as he's pulled away.

"What? Whatever is the matter, Hythlodaeus?"