1. Americans have their own word for 'muggle'
In the original Harry Potter stories we learnt that muggle is the term used for the everyday folk that don't possess magical powers. However, it turns out that American wizards have their own slang term for non-magic people: "No-Maj."
2. All knowing wizards
The magical communities of Native Americans, Europeans and Africans knew about each other long before Muggles/No-Maj "discovered" new countries in the 17th century. The communities were also in contact since the Middle Ages thanks to premonitions and modes of magical travel.