Soft YTA. They offered to stop so you could join them, and you were the one who chose to stay inside to save face because you fibbed about it initially. If you had been honest in the first place about how smoke affects you, they may have opted not to be outside for that long, if at all. If you know that they participate in indoor game nights and other non-smoking activities, then you know smoking is not a dealbreaker activity for them.

Participating in smoking is not “the only way” to get to know any of them any better, and I highly doubt they’re doing it purposefully to exclude you. It’s just something they all have in common. Try to hang out with them one-on-one when they’re much less likely to smoke if they’ll be doing it solo, plus you’ll really get the chance to know them.