What would cause my barely used green bearing to do this?

Damaged during the installation perhaps? Onto the axle that is, not into the car. Did you jump the car?
No, I've barely driven it at all. To the gas station a few times. Probably only 20 miles or so. These are not stock, they are prebuilt axles from dutchman axles. I didn't notice any obvious signs of an issue before I put the axles in but of course something could have been waiting to break.