I would bet a lot that it's nothing really you could analyze in terms of rational thinking but that it's still something that everybody has.

Everyone, including you, do get different feelings from different people. Maybe there's that uncle you're just not that comfortable with to begin with, or your neighbour who always lightens you up somehow. But the problem is that focusing on thoughts and modelling your impression by thinking masks these feelings off. Thus, most people don't realize how their feelings change when they move from place to place and from person to person. The feelings can be seen in your body language but in the worst case you're completely oblivious to them yourself. Typically you just grow a blurred sense of anxiety or ease, much like a moving average of what you've felt that day.

Now imagine you do get a slight grasp of all that, and begin to practice it. Maybe you can find a way to "feel" different people, maybe you observe how your feeling changes when stepping into an elevator with different people each time. Maybe you find some other way to sift through people and try to get a feeling from each one. There are infinite number of ways to practices and they are all equally hard.

Sensing can be really hard because, today, everyone is always going, talking, making noise, and acting busy. It's impossible to deal with a lot and try to get a feel of a person at the same time. I think something similar was described in the article: you need to be out of the focus, you have to have some space around you to make this connection with your feelings. However, for some reason, your body tends to like breathing. Focusing on breathing tends to tone down the active parts of brain and emphasize your sensibility to your feelings going through your body. Maybe that is the reason martial arts emphasize breathing a lot. So, it might be that you find yourself breathing slowly and steadily in the elevator, maybe gazing out to the wall during the ride, and just practice sensing what the feeling is each time, with different people.

The more you practice, the better you get. Usually, as with practice, there are turning points where you just suddenly "get it", or at least you will get a glimpse of it if nothing else. Maybe at some point you begin to associate these feelings with an idea, or rather, an intuition. This is where you learn to put meaning in the feelings. A lot of times these feelings tend to be unexplainable. You don't know how, but your answer is "no". Or "yes". Or whatever you were seeking to know. In fact, the surefire sign that the feeling produces a genuine intuition in you is that you can't make yourself explain it. You're still practicing but now you need to practice trust. You get readings, some of which are noise from your mind and some are signals, from your body and based on genuine feelings, and you need to learn to trust your judgement on which one you heard.

Becoming more sensible is not a game. You can't game it: what you need to do is surrender. Also note that it is absolutely not a one-way street. By changing how you perceive your surroundings and the people out there also changes you. You will not be the same person who is asking about this and who eventually gets the answer. It's also nothing mystical nor magical, it's just something humans can do but very rarely choose to do by a conscious choice.

Foot note: I've been a very sensitive person since I was kid. So has my wife. It seems all so normal here now. Many a years back, it was truly comforting to realize that there are others like me. I've chosen to increase my sensitivity during the early adulthood by relying more on it. What you use will get bigger, I guess it's like what a muscle would do. It's also not a general trait or objective capability: it's very personal. What and how I feel the world is completely different from how Jessica Livingstone feels the world. Or my wife. Or anyone else. But the truths I feel myself are only applicable in my own life, so that is fine.