He overstates the point but is it a valid one?
Some objections I would raise are that:
1 – By what threshold is he saying a country is predominantly one religion?
2 – By what measure is religious affiliation identifiable. Is it merely the census box?
3 – In the Christian context the global church is diverse both in terms of race and culture. Indeed the balance is shifting according to some, if I’m still in the faith when I’m 60, I’ll be unusual in being a white Christian