Boruto and Kawaki have one thing in common. If you look closely, you can see that both of them have similar tattoos on their bodies.
I have baser my theory on this very thing. So, pay close attention to every detail now. These tattoos could signify a lot of things.
Personally it could be because they had the same teacher. It sounds unbelievable but I think there could possibility of this being right. Boruto might’ve gone to train to some other village.