In my opinion, when they say that to most people, I don't think they are "reading" anything. I think they just aren't stupid. If we are calling about a POI, clearly we want them to be long term, otherwise, we wouldn't be calling about said person. So when they tell people "He sees you as long term" that isn't reading your feelings or his feelings. That's just feeding you what they already know you want to hear.
However, SOMETIMES, it's actually the truth. That the person actually DOES see you as long term. I've heard this many times myself, but clearly, those past relationships ended. Also, a person can "see you as long term" relationship material but they aren't ready for anything long term. So then sometimes you have this case of them wanting you to wait around and be available to them for when they become ready, even if that means years from now.