Bard was a huge gambler and he just doesn't have any skills in gambling.
He was playing a game against an old man. He lost everything. But then he wanted to go double or nothing as the old man just wanted to leave to go home to his loving family. Bard placed down the spherical egg shaped orb as his wager. When he lost he was like. "F this old man. I'm going to get this guy." So he went to the fire nation and told them about the old man's new found artifact. As the old man dies and his village set ablaze bard's scumbag revenge is complete. He swoops in to take his spoils only to vanish with it to the stars. Leaving the village to die with the old man.