Daniel gleefully tells Natasha that his interview appointment is in the same building. He's excited to see how her overly scientific brain will deal with the coincidence. When he tells her that it's proof that they were meant to be, Natasha just takes his hand and follows him in. He signs in for his appointment and then leads her to the elevators so they can go to the roof and kiss in private. On the elevators, he thinks that he could never work in a building like this.
Again, when Natasha simply ignores Daniel's mentions of fate and destiny and follows him anyway, it's clear evidence that she's no longer threatened by his belief in destiny. The strangeness of the day has provided her the evidence to accept that destiny possibly exists alongside the meaninglessness of the universe.
When they get to the top floor, Daniel leads Natasha up a final flight of stairs to a door. It's locked and has a sign that says there's no roof access. Daniel says "open sesame" and miraculously, the door opens. It's a security guard who reeks of cigarette smoke. Daniel pleads with him to let them on the roof, but the man doubles over with a coughing fit. Natasha comforts the man and tells him he shouldn't smoke. The man says Natasha sounds like his wife.
When the guard mentally connects Natasha to his wife, it shows again that Natasha is part of a much larger web of connections, even with an older security guard who seems to have little to do with her at first glance.
Daniel shoots Natasha a look to leave the man alone, but she ignores him and tells the security guard that she used to volunteer in a pulmonary ward and his cough sounds terrible. Daniel fantasizes about her uniform as she demands the guard's cigarettes. The man gives Natasha the cigarettes. The man tells Daniel to be careful of Natasha and asks Natasha how she knows that he won't go out and buy more cigarettes. She admits she doesn't, and he suggests that life doesn't always go as planned. The man tells Natasha and Daniel to stay away from the edge and to have fun.
Natasha very clearly cares for other people, as evidenced both by the way she interacts with the security guard and the fact that she used to volunteer at a hospital. This again shows that Natasha hasn't always leaned on rationality as a crutch to keep her isolated; she once used her interest in science to help people. This is more proof that the world is made up of an interconnected web of people.