I have no idea what thread anyone is talking about, but my personal opinion on all of this is that while thoughts alone are not rude...thoughts expressed on here can be.
Any time you give voice to a thought, even if you're talking about a person that nobody you're talking to knows, you run the risk of being rude. I'm not going to lie and say I haven't said some pretty mean and nasty things about people to my select few confidants, but I still think it's important for anyone who wishes to live in a more civil world to sharply curtail that sort of thing.
So if I see a post where the OP has put in a lot of unflattering physical descriptions, for instance, that have nothing to do with the matter at hand...I am, at the very least, going to think less of the OP. If it seems egregious enough, or related enough, I might call them out on it. And in that case, I would in one sense be calling them out on their thoughts. I wouldn't be calling them rude in the situation they described, but I would be calling them rude for the situation they were in on the thread.
I think what this boils down to, sometimes, is that there seems to be the idea that in order for rudeness to occur, it must have a victim (so to speak). It must be perpetuated against a person or a group of people. But I don't think that's necessary at all. It is possible to behave rudely even when nobody is directly harmed by that rudeness.
And since this is an etiquette board, and we are all presumably looking to improve our manners, I think it is absolutely fair game to point out when another poster is expressing ideas that are rude. Even if they didn't express them anywhere but here.