I've been on the other side of that (not google), taking people to lunch who are interviewing. Usually you're picked because they're from the same country as you or something like that. At least where I work it's not like those messages. Instead it's lunch because food is good to have, and if you were lunching with them you weren't involved in the interview process at all, and it gave them a person to ask questions of and get an unbiased-as-reasonable response. If there were real red flags I'd probably raise it, but otherwise I had no contact with anyone in the hiring process regarding that person at all.