During the first card game at the firehouse, Montag is already beginning to think about his job and his life, and how the world came to be the way it is. He asks Captain Beatty if "it was always like this". In other words, if firefighters had always started fires, if books had always been banned, etc. This is a direct result of Clarisse's influence, as her friendship has prompted Montag to question his world.
The other men are shocked when Montag asks this. They point to the established history, the one they were taught growing up, and which they have swallowed without doubt. They bring out their rulebooks and show Montag the code of the firefighter, and laugh at his audacity. To them, he's just a troublemaker. They're content with their lives, and they don't like anyone threatening that. Like Mildred, they're not willing to admit unhappiness or any kind of discontent. But Montag is different. It is this willingness to question authority that will lead Montag done the path to rebellion. Eventually, he will be forced to embrace his dissent and escape from the authoritarian society.
When Montag is playing cards at the fire station with Beatty and the others, he asks what happened to a man whose house was burned the week before. Beatty replies that this man was taken to the asylum, on the logic that anybody who goes against the government must be "insane."
Montag's question is significant because it is the first time that he has considered censorship from the perspective of the criminal. At the beginning of the novel, for example, Montag states that it is a "pleasure to burn--but his feelings are now changing. He begins to realize that his actions as a fireman have moral and social implications.
In terms of the plot, this question develops the idea that Montag is beginning to change. Specifically, he is questioning the status quo. This sets the stage for his meeting with Faber and his plan to bring down the fireman system from within.