The first man, I decided, was waiting for someone and was very clearly uncomfortable with the idea that he was sitting alone in a public place. His right leg was shaking rapidly (my right leg started doing the same thing as I watched him) and kept giving off signals that could only be interpreted as a mixture of anxiety and outward gestures to let people know that he was waiting for someone. He also kept taking out his phone, fiddling with it, and putting it back away. I was behind him, so I noticed that all he was doing was compulsively flipping back and forth between the home screens on his iPhone. Sure enough, a woman with whom he seemed well-acquainted with showed up five minutes later to join him, and he calmed down.
The second man had no scheduled guests beside his waiter and was calm as could be. He just sat, unoccupied, and enjoyed his meal and coffee alone while mildly observing his surroundings. He even noticed me glancing at him and offered a smile as if to say that he knew what I was doing. I smiled back.
The reality is, and this was one of the points of the article, that I hadn't even noticed either of them until I had intentionally given myself a reason to.