The abilities that we have seen Kawaki using like extending his arms and changing the shape of his body into weapons. I think these sorts of abilities are down to his modified body. We don’t know yet who Kawaki’s creator is but this creator of Kawaki was praised by one of the brightest minds of Konohagakure, Katasuke.
As Kawaki is superior to Mitsuki who is Orochimaru’s best creation, it is clear that Kawaki is not Orochimaru’s creation. In my opinion, he will surely have a connection with the scientist who has created Kawaki. Orochimaru has to be involved in something like this, that’s what his character demands. So, I think that even though Orochimaru hasn’t created Kawaki but will surely have some sort of role in Kawaki’s creation.