This may sound like a dumb question but does anyone know if people that are double jointed in their fingers can do better and more amazing XCM or is that just a dumb question on my part. 
Devo is double jointed, but it matters on how much you practice.
It simply means that your joints (and the surronding muscles, tendons and ligaments) are unusually flexible, allowing you to bend or rotate them in ways that other people find impossible and painful.
Basically, you can bend your joints further than other people can.
Wait... I thought double jointed is when your left arm is equally strong has your right arm? As in you can both write with both hands and stuff like that...