The article specifically mentions olfactory similarities being pro-friend and immune differences being pro-friend. It didn't mention ethnic markers like melanin, face shape, nose width, ear size, or relative toe length at all. In fact, it said they attempted to control for racial and ethnic differences. How well that was accomplished wasn't really made clear in the article.
I can imagine that whether or not cilantro tastes like soap, whether or not you love the smell of books, similar allergies, and if you can stand to eat spicy foods goes a long way toward the likelihood of friendship. There are bound to be social factors, geographic factors, and other factors. This study is just pointing out that friends are likely to be more similar in certain ways than people who aren't friends. Don't jump to too many conclusions on just the summary article about the study.
I can imagine that whether or not cilantro tastes like soap, whether or not you love the smell of books, similar allergies, and if you can stand to eat spicy foods goes a long way toward the likelihood of friendship. There are bound to be social factors, geographic factors, and other factors. This study is just pointing out that friends are likely to be more similar in certain ways than people who aren't friends. Don't jump to too many conclusions on just the summary article about the study.