Humble means "modest; without an excess of pride." A person who brags about being humble may have too much pride in being humble to actually be humble.
Sometimes fictional characters try to earn favor by saying "I'm just a humble man in search of..." when it is obvious they are the opposite. Truly humble people keep quiet about their accomplishments and the good things they do. Humble can also mean "low in station or quality." If you come from a humble background, you didn't grow up wealthy, and if you live in a humble apartment, it isn't overly grand or showy.