I still think the point here is that these are women who haven't heard about Damian and know about Dick but don't consider him Bruce's son, rather than that they not only don't know about Damian but also don't know who Richie Grayson is within their social circle.
The women seem like gold-diggers and/or extreme social climbers. So it would only make sense that they know the hot rich guy at the party is also the son (and heir--that's the part I think would REALLY get their attention) of Bruce Wayne.
It would have been kind of interesting, maybe, if the woman that wants to get 'Richie's' attention would have referred to the fact that the grown one's a son, too. With a lot of social status and money.