Lemmy and kbin communicate using activity hub protocol, that doesn't mean they communicate with app using the same protocol.
So it is not necessarily trivial to let a Lemmy app support kbin.
Exactly this, they don't use the same API. It would be a pretty big effort to get Kbin working on Jerboa, it's likely that mobile apps specific to that will pop up soonish.
API support in KBin is currently on the roadmap but disabled (for now). Hopefully once there's a working API for KBin, an app will materialize. I have my suspicions that there still won't be interop (you can use a Lemmy app for KBin or a KBin app for Lemmy) for a long time, but I definitely think it will make KBin instances a more attractive link aggregation community solution
If you're subscribed to a kbin community, you can browse it in jerboa.
This is correct. As I understand it, Jerboa is just connecting to your Lemmy instance. So anything you can subscribe to through that instance, whether it be another Lemmy instance's community or a kbin magazine, will also appear in Jerboa. I'm not sure how easy it is to find a kbin magazine in Jerboa since it seems kind of hit or miss even in the web interface.
