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

In my experience the 1st Gen bearings didn’t last me long, probably around 1 year of use. I did remove the thrust block and the install was done correctly, including the pressing on of the bearings. Replacing the defective 1st Gen Bearing to the 2nd Gen bearing has lasted me over 20 years.
As far as 8.75 housings being straight in my experience making 451HP and 589Tq at the rear wheels, the axle housing does twist and become deformed. I can visually see spring perches bending, axle housing bending, kinking below the U bolts (especially on the passenger side). Transbrake, blower, nitrous, 3800 pound race weight big tires, etc....
We really don’t know what the OP’s installation process consisted of.......
With that said, the 2nd Gen Green Bearings are a better design.