It does look cast from the picture, but it could be forged and they shot peened it to increase the spyders strength. I believe shot peening removes stress risers in the outer surface of a materials and prevents stuff like cracks. I'm sure a mechanical engineer could freshen us up on if what I said was correct.
Very hard to tell in the picture cause of the bad angle and the quality.
It's good to see Polaris finally address issues, if I couldn't get an M858 I would buy a Polaris now. That 4 year warranty is a nice plus too.