There are other ways in which Bilbo is a hero, too, aside from the obvious saving of the dwarves. If we look at chapter 5, "Riddles in the Dark," we see how Bilbo's encounter with Gollum adds to his heroic traits.
At the beginning, the hobbit and the creature engage in a battle of wits for Bilbo's life. Gollum has lost the ring; Bilbo has stumbled upon it. And it is the ring that ultimately allows Bilbo to make a last-ditch attempt at a riddle to keep him from being eaten. Gollum, however, doesn't see it as fair.
Arguably, it isn't. Asking about an object in a pocket is more of a guessing game than a riddle, and it angers Gollum. Bilbo ends up using the ring to escape Gollum, who is hastily chasing him. Because the ring is on Bilbo's finger, he eventually comes face to face with Gollum at the exit. Bilbo has the advantage; he has a reason to kill Gollum (for trying to eat him), but he doesn't:
He must get away, out of this horrible darkness, while he had any strength left. He must fight....
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