I know a QA ex Google engineer that refused to ever work for a company with a cafeteria again solely because he got tired of people complaining about food that was free. It annoyed him that much.
I see the general principle guiding this and agree with it, but "free" food from an employer is just another form of comp and complaining about it's no more ungrateful than complaining about health benefits or salary. It's not like complaining about a Christmas gift or something.
You're not wrong, it was more complaints about food he saw as objectively delicious. His go to would be him clowning around like "wah they had this cut of steak but I like filet more."
Heh, OK, that would grate more than a little, makes more sense now.
He should read up on the economic principle, tanstaafl (there ain't. O such thing as a free lunch), then it won't bother him so much.