Could Mumford be wrong that "discipline" was required for grinding?

Here's illustration of the kind of classic problem faced by Archaeologists as they try to discern the relationship between society and technology: the research thinks of X as the necessary condition to using a certain technology, when Y is really the reason, but there is no evidence of Y being present over X, so X is mistakenly assumed to be the reason.

For example, Mumford writes, in describing the process of grinding to make stone tools was "the patient application to a single task, reduced to a single monotonous set of motions, advancing slowly, almost imperceptibly..." (p. 137.2.4); And later, "Those who were ready to submit to this discipline would, it seems likely, also have the patience to watch the same plants, through the processes of growth, season by season... to achieve the same anticipated result." (p. 138.2.2)

He argues that establishing the patience to grinding of tools allowed people to soon after that grind grain, and thus, make bread (er, of a sort!). But is "patience" the only explanation? Could there be other differences between groups that would explain why some did grind [though without the bump, mind you!] and others didn't?