The bending ability of Rean's Black Star was something he added in the Realm of Gods. He got the study material in the Blacksmith Hall back in the Lukimira Sect and soon found about this method. Yes, Roan's White Star also had the same ability. It's just that Roan hadn't used it yet.
Knowing that Rean's sword could bend and defend against were two different things, though. Luval was forced to position his spear further away from his body every time he used it to block a hit from Rean to make sure he wouldn't get hurt. But even then, there were times where he miscalculated and got a few cuts in various spots, thanks to it.