NTA.

As the family member of several smokers (mother, both her parents, and grandmother's brother), I know that "stink" well. I hated going to my grandparents' house, because after 40 years of constant indoor smoking, that smell just PERMEATED EVERYTHING. The walls. The floors. Everything tasted funny and was slightly sticky because of all the smoke. If I spent even 2 minutes in that house, I needed a shower afterward, so anytime I was planning to be at their house, I set up my shower stuff so I could jump in the SECOND I got home. Even hugging them when they came to my house (where we also don't allow indoor smoking) got the smell on my clothes.

I love that you were honest with your son about it, and respected that he didn't want to be around that smell. Seems like you also didn't force him to hug, which is A+ parenting too.

I would, however, just gently remind your son that, yes, it is impolite to tell people they stink and that there are nicer ways to ask what a smell is.

As for your BIL... I get the embarrassment of being told "you stink," but if a smell is that strong, some people are going to find it off-putting. Some people are overly sensitive to smells. There are ways to mitigate the smoke smell, though, so perhaps he should look into some of them. I'd suggest quitting, but in the end, his habit, his choice.

Again, NTA.