Bantu means people (apparently specifically that of a people from central Africa), so I think he’s basically saying, ‘Pierre I’m your dad, I’m wise, we are people and there is a hierarchy in this family, listen to me, I choose what you do, moolah is on its way’.
The grains is a reference to reaping the rewards of a crop, i.e., a new contract, whether that be at Arsenal or another club it waits to be seen.
Edit: We also don’t know to what extent Auba’s dad represents Auba’s interests, this could just be a family member publicly intruding in an area that isn’t theirs to intrude in. We just need to wait and see. His dad is his agent.