You're here now. A further implication that Snake shouldn't be there, that he's out of place. However, being invited as Vena's personal guest takes him by surprise. Or maybe it shouldn't? He doesn't know anything about Vena (just as Vena doesn't know anything about him). Maybe that's just a good way for the host to make sure his party doesn't get derailed by an unexpected guest.

"Oh, thanks. I know you don't know me so my word's probably not good for much, but I really don't plan on making any trouble for you or for me. But I gotta say, you're guests are so interesting!"