In "Fahrenheit 451" what did Montag discover about Granger and his friends?The answer is not: They memorized books; it's something else.
Upon first appearances, Granger and his friends seem to be a bunch of vagabond homeless people, hanging out on the fringes of society, down on their luck. As Montag talks with Granger, one of those men, however, he realizes that many of these men have chosen to live this way, or have been driven to this life because of the restrictive, stifling, and sometimes even threatening structure of their society. Granger is not an illiterate and down-on-his-luck homeless person; rather, he is well read, intelligent, wise, and content with is lot in life on the fringes. He has even written a book called "The Fingers in the Glove; the Proper Relationship between the Individual and the Society." There are professors and authors galore in the group of outcasts.
Montag, no literary man or professor, feels intimidated by their smarts, and states so; he is just a simple fireman. Granger confesses that back in the day, he "struck a fireman when he came to burn my library," and that ever since that day, he's been on the run. That is quite a discovery, because Montag himself is a fireman. Granger is not afraid or intimidated though--he asks if Montag wants to join. There are no hard feelings. The men unite together, with their memorized books and wisdom, and will be the force that hopefully rebuilds their society better than it was before. I hope that helped a bit; good luck!