Why does my Siamese cat meow about every time I touch him or try to pet him?

Whenever my Siamese cat is laying down / trying to sleep I try to pet him and he meows and I know one reason might be because he doesn't want to be bothered because he is trying to relax / sleep and I also know that another reason might be because he is a Siamese cat but are there any other reasons as to why he might meow about every time I try to touch / pet him?