On the face of it seems highly unlikely to me that two groups had a level of contact that was enough for farming knowledge to be spread between them but not eno

On the face of it seems highly unlikely to me that two groups had a level of contact that was enough for farming knowledge to be spread between them but not enough for genetic flow between them. Farming is not a simple technology. It's a way of life and encompasses a package of technologies. And the crops and animals raised in the respective origins could be raised in both locations so there's no obvious reason why diffusion of the farming knowledge would not be accompanied by the spread of those crops and animals.