And certainly it's American chains that spread said McDonalds fries all over the world. It's also a crucial element in famed (or perhaps I should say notorious) national dishes of the UK, Canada and probably other countries. That doesn't stop it from being originally Belgian (okay, the French might have a claim too, it's not entirely clear), or from being a Belgian symbol in much the same way that you might call something "as American as apple pie".
Let's face it, besides arguably Tex-Mex there isn't that much in American cuisine that is completely American in origin and isn't inspired by something brought from abroad - that's where your culinary genius is, in combining and reinventing all those things brought from different countries, and then more often than not re-exporting the new Americanized variation to the country of origin to compete with the original. Whether it's pizza, waffles, fries, ice cream, whatever.