A friend of mine received a brand new phone that's already rooted topic

Hello. So I have a friend that received (as a gift) a new phone and he already has SuperSU installed. I was surprised when I saw that app in his phone and asked him what that was. He said he had no idea. Then I asked him if the app came with the phone and he said yes. I was again surprised. How is this possible?

BTW the phone is chinese. Not sure if it has to do with that.

Thanks!