There's no social dance to it. Just don't be a leech, but accept help when it's needed and don't offer help unless you're genuinely willing to give it.
There is. What constitutes a leech varies from person to person, from culture to culture. Accepting help could easily lead to resentment, it's entirely possible they were offering help to seem generous while simultaneously expecting to be refused. Offering help at all could be offensive because you're in a position of strength while they're in a position of weakness, it implies they need you, ingratiates them with you, puts them in your debt.
Correctly navigating these waters requires instant judgements based on huge amounts of social information like status, reputation, personality, context, non-verbal cues like tone of voice and body language. It is difficult to do this deliberately because during conversations there is not enough time to deeply analyze anything. It's best left to an uncounscious mind honed sharp by repeated practice.
Every interpersonal relationship has its own dance, no matter where you're from. That's what socializing is.
And sadly, those not born with a neurotypical brain are very bad dancers.
they were offering help to seem generous
Then don't offer. In that hypothetical situation I am in need. You are exploiting it for your own betterment of looking generous to the rest of the community. Consider your selfish bluff called when I accept!When out having drinks, it is considered (1) rude to let your friend's drink go empty, and (2) rude to refuse your friends offer for a drink.
Is this accurate? If so... one can imagine how this can get pretty messy!
As for (2) I don't know any culture where if a friend asks you to meet up with them that there isn't some expectation you'll accept the offer and if you can't you'll at least try to make the friend feel you'd really like to but for whatever reason you can't right now. If you just responded "no, I don't want meet" I'd except after a few such responses you'd no longer be friends in any culture.
I have a good friend whose parents are from Persia/Iran. He told me about this culture after we knew each other for quite some time. Even though he has never lived there, he often still has a hard time not to do this, which has resulted in some funny (at least for his friends) or uncomfortable situations over time. Knowing this, many things I ascribed to his character alone suddenly made a bit more sense.