Yeah, it's a sexist comment implying she isn't either qualified to be at the conference, or mistaking her for a passerby who is unaffiliated, and should consider working there. Either way, I don't find sexism funny. Dunno why anybody would, but hey, I'm just some guy on the internet, so you do you.
Without any context it or history its just kinda dickish? Like maybe a good burn to a rival in some sort of relevent scenairo but this just sounds like an attempt to belittle someone by "mistaking" them for something "lesser" then when called on it they double down?
Strikes me as grade school level bullying at best 🤷
I don't think it's that funny, just a sad defense for not being able to recognize that someone belongs at the conference instead of among the customer service staff.