You can answer this question by reading Chapter 6. On page 110 in the paperback edition, Diamond tells us that storing grain is one step that pushes hunter-gatherers towards full-on food production. When hunter-gatherers start to store grain, they become more anchored to the place where they live. They have gone to all the trouble of creating facilities to store grain so they are much less likely to want to move away from the place where those facilities are. This makes them more rooted to one spot and makes them depend more on the resources that can be gotten near to that spot. They can no longer move around as much to hunt and gather. They have, therefore, taken one more step towards becoming a true farming society.