It is, but both are part of "fediverse", so they share content.

In short:

Both Lemmy and Kbin use a tech called "activityPub" that allows platforms to share communities and content. So it's not only different lemmys that share content, its also other platforms that implement this tech.

Once Kbin fixes its federation (the implementation of this tech), you'll see the community here on Lemmy as if it were Lemmy community and can interact with the users same as with other lemmy instance users.