I think this is a bit of a fallacy. There was plenty invented in pre farming times, just these inventions were tailored to the task at hand which was hunting and foraging rather than other goals. For instance, the spear thrower. With that invention the act of spear hunting became orders of magnitude easier for less able bodied people. Spear throwers can be used to send a projectile 100m, and as fast as an MLB pitcher. You can imagine how this might have significantly improved the kill rates of the hunt, and could be thought of as significant of an invention as perhaps the plow was.