JC, I would speculate that the stock was got out to this shape rather than bent except that I can't detect dark areas of end grain which should border the depression or cove fore and aft if it were worked in that way. If it was in fact bent, it must have been a more complex job than a twist to the wrist. I think it would require a fulcrum between thumbhole and heel about which the stock was bent after shaping. Who knows?

jack