What was different about the fire Montag saw after leaving the river?

I'll answer the first part of your question and let another editor answer the second.

In Fahrenheit 451, after escaping the city and the mechanical hound brought in to hunt him, Montag follows railroad tracks after getting out of the river.  The fire he sees is a campfire, and he notes that it is different from fire as he had experienced it, it was a "different thing."

This fire was warming, not destroying.  He sees hands near the fire, being warmed.  He never realized that fire could give back, not just take.  He notes that even the smell of the fire is different from what he was use to.