Kbin is a different application, another content agregator suitable for leaving Reddit. The thing is, since we all use the same protocol to communicate (ActivityPub), these two completely different applications can talk to each other :)

They're functionally very similar but are two seperately developed pieces of software. The lemmy devs are tankies and many would prefer to completely avoid using something from them. I don't believe there's anything to worry about, as the devs can't control individual instances.