Is kissing in the lips normal for best friends?

I met this girl during real singles tours and we started dating right after we hit it off. I really like this girl because she’s one of a kind. She’s fun to be with and we both like Sidney Sheldon’s books. Two weeks later, she let me meet her guy best friend. We decided to have a cup of coffee with her best friend. While this girl and I were talking about outdoor activities, waiting for the guy to come, someone suddenly grabbed her arm to hug her. I was shocked. Little did I know, it was the guy we have been waiting. So, she introduced me to him and we started chatting. I noticed that the guy is very clingy to her. He often held her hands and he even kissed her lips when he bid goodbye. Is that normal for best friends to kiss in the lips or there’s something going on between them and I am just a villain in their story? What do you guys think?