It's American to my British ear. I think they sometimes distinguish 'pizza pie' as being the deeper-pan Chicagoan style, which to be fair is a lot more like what I would call a pie than what I would call a pizza. (But also not really either.)
"Pies" is most certainly not American. I have heard that it is supposedly specific to New York, but if you watch Friends (set in New York), you'll see frequent references to the Joey Special, "two pizzas".
It's always possible that there are zero people who think of "pies" as an appropriate way to refer to pizzas, but the myth persists that weird foreign people do it. People will believe anything about weird foreigners. Or there might be weird foreign people doing it right now. It's hard to know.
Not? I'm confused who you're saying does call pizzas 'pies' (or 'pizza pies') then?
I assure you some Americans certainly do, wherever they got it from, 'American' or not. I've only been exposed to it via American film/TV, including food shows - most recently Somebody Feed Phil in Chicago.
I've never heard it in the UK. I'd be surprised to learn that Italians call them something else too that in other contexts translates as 'pie', but I'm not sure how relevant that would be anyway.