1. Where grains used for food or they just fell off the grass used for example as fire fodder or bedding?
2. If they were eaten, how much and how often? (not feasting I assume, looks more like starvation diet)
3. Modern wheat is much worse
4. How healthy were tribes who ate grains comparing to ones that didn't?
5. I bet that even the most devoted consumers of grain preferred meat or at least ate some part of diet as meat and animal fats.