I would totally see myself doing that. You do me a favor I‘ll do you one. Simple as.

Sometimes true but not always. I've had coworkers from the UK all the way to the middle east who were always happy to buy drinks and were more generous, I suspect many from across the commonwealth, and greco roman world tend to take gifts of food more fairly.

Much of China having gone through multiple famines tends to have a different food culture though which probably makes people come off rude to each other