Montag says there are too many of us. In what ways is he wrong? In what ways is he right?

In this part of Fahrenheit 451, Montag is reflecting on the world's population and the disconnection and alienation the large population causes. He is in the midst of a crisis because his wife, Millie, has overdosed on pills and a medical team came to their home and saved her. The distance between their family drama and the doctors' detachment is shaking him up.
In the following sentence of the passage he comments, "Nobody knows anyone." The doctors don't know him or Millie. In these specific observations, he is right.
The depth of his alienation is pointed out in the next three lines as he becomes increasingly upset:

Strangers come and violate you. Strangers come and cut your heart out. Strangers come and take your blood.

Those particular strangers actually saved her, so he is obviously thinking more broadly about the way his society destroys people.
As the story progresses and we see Montag change, it becomes clear that he was wrong as well. He goes through painful experiences and ends up "taking blood" by killing another man, although not a stranger. Nonetheless, among the billions, he finds the people he needs to know, people who were once strangers: the book learners who become his true community.