As Montag changes, the other people he interacts with react largely with disbelief. Since everyone is used to thinking, feeling, and expressing the same ideas and beliefs, they literally cannot understand how Montag can change his personal self so drastically.
Montag moved his lips.
The women jerked and stared.
"How're your children, Mrs. Phelps?" he asked.
"You know I haven't any! No one in his right mind, the Good Lord knows; would have children!" said Mrs. Phelps, not quite sure why she was angry with this man.
(Bradbury, Fahrenheit 451, Google Books)
This reaction is typical of the people living in that society. The concept of personal conversation that doesn't hinge on television programming is so alien that it causes feelings of anger and distress. Mrs. Phelps feels angry that Montag has even posed the question; she cannot fully answer it, and has no pre-programmed or societally-accepted response for him. Normal conversation, with branching topics and subjective opinion, is almost unheard of; as Montag expresses individual, non-approved opinions, he is treated like a person who is swearing in Church. Only his boss, Beatty, treats him with amusement and a little contempt; it is hinted that Beatty has many of the same feelings, but deliberately suppresses them to keep his job and position in society.