Genetics are so weird!!!

So my boyfriend has some Native American, a tiny bit of Irish, and some more European random things in him. He is VERY olive skin toned. All year round. In the summer he tans better than anyone I’ve ever met. He also has very dark thick hair on his head and a full dark beard, light eyes but here is the thing.... all of his arm hair and leg hair is blonde!!! 100% blonde! How does that happen? Genetics are so fucking cool!!!!!!