My understanding believe kbin federates with three rest of the fediverse, (activity pub?) including Lemmy and mastodon, but not necessarily the other way around for their users.
From here, you should be able to see and comment to users on Lemmy insurance, as long as they are not blocking federation with your kbin instance.
Is there a way to track the activity change/traffic for Reddit? Especially now, given that 3rd party API access is mostly cut off.