I don't think the Power Pole is made of dragonbone.
Presumably Yama claiming to have gotten it from a dragon is a reference to Journey to the West, upon which the first story arc of Dragonball is loosely based.
Sun Wukong(Or Son Goku if you prefer the japanese to the original chinese)'s staff, which changes size and shape at his command, was obtained when he barged into the palace of a dragon king, who lived in the bottom of either a river or the ocean depending on which version of the tale you read, and demanding a weapon worthy of himself.
I'm actually seeing a lot of Wukong in Yama... Like, everything from Wukong that didn't go into Goku.