You don't really need to worry about it... some types of kisses are normal greetings in some cultures, and it's not all like it is on TV and movies. sometimes two people who like each other kiss when they feel attracted to each other, and sometimes they do it just to feel what its like.
if he was kissing her when she didn't want too, that's a different story altogether. but kissing because you don't him too isn't really all your business. you don't own somebody just because you like them and they like you.