When I interviewed at a Google outpost, a good-cop employee they mistakenly thought had a connection to me took me to lunch (message: forget about the bad-cop interviewer you were just with, you're among friends, loosen your tongue so our spy can report back) in their cafeteria (message: look at the free food perks you'd enjoy), and initiated a conversation with an visiting economist there who then spoke of something oddly relevant to my research interest at the time (message: look at the interesting people and collaborations you will bump into every day).

Your interview lunch experience sounds like message: this is what it's going to be like, and we don't care if you join us.