The term academy product is really flawed anyway and there is no consistent rule for it.
Busquets/Puyol/Pedro has arrived at the age of 17, and we consider them Barca product, while considering Cesc,Alba & Eric Garcia as La Masia product too for whatever reason, despite leaving in younger age than the former players joined Barca.
Most youth player plays in many clubs anyway, it is usually the one that gave them the first team debut that will benefit from them the most.
As for Foden, he seem to be the first academy player , that he didn't coach in B team, that has developed into something long term for his own team.
Good for him and City, this generation of English players could be distained for big things.