And that's because the members here are from all over the world and live in very different societies with very different social norms.
Asking a question like this to a group of strangers on the Internet will result in wildly different opinions and in most cases, you won't know any more than you did before you asked.
Consider though, this is a group of crossdressers and many have an agenda to promote crossdressing. It's not the same as asking a bunch of "ordinary" people.
My opinion - It's none of your business and you may embarrass him by mentioning it. I would not say a thing and treat him the same as if he was not wearing panty hose.