Humility isn't a lack of confidence. Meekness isn't the opposite of having self-esteem. Jesus Christ said the meek "shall inherit the earth." We wouldn't think that at that point the earth will be filled with frightened people who hang their heads low.
Moses was called the most meek of all men, yet he had a commanding spirit about him. His strength came from his reliance on the Lord. He had full confidence in what he could do with the Lord's help. Moses's righteousness made it possible for the Lord to work miracles through him.