"Skinny guy" here, and I can tell you that it can go both ways. I have had people who barely know me ask "Wow, how much do you weigh?" (as if it wasn't enough) I highly doubt they would ask a fat person the same question. I can't help it if I'm skinny, I've always eaten as much as I can. I would never make a fat jab at someone, especially someone I didn't even know. I say the comment was probably a harmless compliment.