In Part Three, the hobos that Montag meets aren't really hobos at all; they are a group of men, mainly former college professors, who had to flee the city because they are wanted by the authorities. One man, for example, says that he hit a fireman who came to burn his books and has been running ever since.

These men identify as famous authors or pieces of literature because that explains and defines their new purpose. They are book covers: men who have memorized a book so that, one day, it might be written down again for a new generation to read. When Montag joins them, he becomes the Book of Ecclesiastes because he has committed the text of this book (or most of it) to memory.

These men are, therefore, waiting for society to break down so that they can step forward and help to rebuild. They want to create a new society in which book-reading and learning are not prohibited. For them, the future is the focus. This explains why Montag immediately joins them. 

The hobos that Montag meets are modern-day Homers, memorizing books to pass their knowledge along as a new oral tradition. They each memorize books in their entirety, using mental techniques to close those memories off until they are needed; this prevents forgetfulness and degradation of memory. When Montag meets them, they introduce themselves in literary terms:

"I want you to meet Jonathan Swift, the author of that evil political book, Gulliver's Travels! And this other fellow is Charles Darwin, and-this one is Schopenhauer, and this one is Einstein, and this one here at my elbow is Mr. Albert Schweitzer, a very kind philosopher indeed. Here we all are, Montag. Aristophanes and Mahatma Gandhi and Gautama Buddha and Confucius..."
(Bradbury, Fahrenheit 451, Google Books)

This odd method of identification allows the men to quickly know who has memorized what, so as to avoid unnecessary duplication. While some duplication is necessary, in case of sudden death, too much is redundant. Another reason is to keep their real names hidden; while the book-burners might recognize the names, others will not, and so they can travel in anonymity by using their literary pseudonyms. Finally, it allows classification along philosophical and genre lines; a person who specializes in political writing will leave religion to others, which a science expert will avoid science-fiction, so as not to get confused.

The hobos are different because they are men commited to books and the knowledge contained within them.  They have memorized sections of books to insure the information is not lost, and they plan to pass the information onto their children so it is not lost.  They identify themselves by authors or pieces of literature because those are the things they have memorized.  Each man is responsible to remember different texts so they are not lost.  Montag himself begins to memorize Ecclesiastes at the very end of the novel.