I think it means the group of people that Facebook deems as appropriate to avoid causing too much trouble for itself, which is quite different from the set of p

I think it means the group of people that Facebook deems as appropriate to avoid causing too much trouble for itself, which is quite different from the set of people/data covered by GDPR. If facebook puts you in the American group, then tough luck - though you can and should complain to the regulators/courts.