Because through Newt, he was exposed to the wizarding world, but because of the laws of the wizarding world, these memories were later erased, resulting in Jacob not being able to do magic, and not being able to do magic is called a muggle. Muggles and Muggles: Both are wizards' names for "ordinary people who can't do magic", and in Harry Potter they are called Muggles. In Harry Potter, they are called Muggles, and in Fantastic Beasts, they are called Muggles. "Muggles" can be seen as the New York wizarding community's term for ordinary people, as even Newt is confused when he first hears it, and then says "Oh, we call them Muggles". Jacob in the movie is a Muggle.