What breed is my friends blue rescue cat?

My friend has always wondered if her blue cat, who she got from the local shelter, is not a domestic shorthair like the rescue said. He definitely resembles a Russian blue, but I’d love to get you guys opinions on what he might be! He is 13 pounds, but a little overweight. In terms of personality, he is a pretty chill and snuggly cat, but is very playful too.