Earlier quoted context omitted.
> It really is true that there are unspoken codes and mores to follow, and it was uncomfortable when I didn't Any examples spring to mind?
I can't speak for OP, but a big one is how to deal with the check at a restaurant. For people who are lower/lower middle class (or at the least not financially secure), you pass around a receipt and take turns deciding who owes what. In the middle/upper middle class, there is an unspoken rule the check gets split, and anything else is awkward. In the upper class, oftentimes one person will pay for the check and it's…
That's how it's in my country for all classes, poor or rich.
When friends go out, someone and pays for all the others (and someone might ask to chip in or pay themselves, but the first one doesn't take no for an answer).
Next time you see each other, the other person can pay, but no one keeps any very specific tally ("I paid 3 times, you paid 1") -- that would be considered tacky and cheap. That said, if someone systematically over many meetings never takes initiative to pay that the rest start considering them a cheapskate (but never giving specific tally or anything -- it's more from the feeling "never remember you paying").
Anybody insisting on splitting the bill, or obsessing over who ordered what, is also seen as a cheapskate.
That's how it usually goes among people with regular income. Now, sometimes, when the company is comprised of people that might be students, unemployed, etc, they more often agree to split the bill. But in this case too, obsessing over who bought what is considered rude, and usually it's just a simple bill/persons split that's paid by all.