I think he might mean American made cheeses and not American cheese specifically
cause a lot of chains will use stuff like mozzarella but they use a highly processed pre-shredded version that is full of preservatives and starches to keep it from clumping while it is stored
both of which do their job at keeping the cheese edible and easily spinkable as a topping, but also make the cheese less tasty and screw with the consistency so the cheese doesnt melt right
if your cheese isnt stretching when you take a bite of hot pizza, then they werent using good cheese
I've seen an abomination "pizza" with American cheese on it. :(