I think this was a scene very well achieved, it created a lot of tension.
I think Mr. Archer was trying to be polite, while the Vulcan was rude in his one-word responses.
Mr. Archer never meant to ask the question directly (are you spying on us?)
until he was forced to do so by the rudeness of the Vulcan.
During the entire scene I was under the impression that captain Vanik had a secret agenda.
Why did he accept an invitation to dinner, only to later claim that he had already eaten? That's totally impolite.