The first detail is in the first sentence. The city is silent. Since people make noise, that means that there's essentially no one out. This is reinforced a few lines later when readers are told that Mead is "as good as alone" in the world.
That means that he is the only person alive--or at least, the only person outside of a house--who sees/feels the mist of the evening, feels the uneven sidewalk "buckling," feels the frost of the air, etc.
Look at how specific these details are. That too creates a sense of isolation: Mead sees the world more vividly than anyone else in the story (which would be anyone else in the world, functionally).
In the second paragraph, you see that Mead's habits are uncommon, and the details reinforce this. He goes to the graveyard, and sees "phantoms." They are "sudden" and "gray." That's rare, and he's the only one who sees them. That's true isolation.