That National Geographic article overlooks that fact that while man may have eaten oats pre-agriculture, they would have been eating wild oats they gathered, so I would imagine not in large quantities. Kind of like the honey, tubers and fruit they ate.

Pretty sure a metabolically healthy person who is very active (like Paleo peoples would have been) can probably tolerate wild oats, etc. in limited quantities.

I don't think this discovery says much about the healthfulness of a Paleo diet.