Isabelle, I think Ellen in the conversation context (we are discussing USBH profiles) uses "European" as an "ethnicity", like e.g., Afro-American, Asian, Latino-American, whatever.
Of course, for us European (citizens) this looks like a vey weird use of "European", since we know well that Europe has been over the last ten thousands years (at least), and is still today, maybe more than ever, a land of migration and (willy-nilly) population mixing. To speak of "European ethnicity" in Europe is at best a fuzzy concept, if not a totally fantasmatic one.
And yes, we and many other European WikiTreers have been saying over and over here on G2G, that WikiTree is definitely too much US-centric.