Kbin doesn’t have a public timeline like Mastodon does. Everything is part of a Magazine or Group which Mastodon doesn’t have. It’s a very different model from microblogging.
For example, from a kbin account while logged in to kbin, a person could have tons of content they want to see by subscribing to magazines without ever subscribing to a user account.
Fedilab, from what little I understand, doesn’t actually “follow” an instance in the strictest sense. It basically “looks” at the other instance’s public, local timeline similar to what you would see from a browser that opened up the site (without being logged in to that site) and pulls from there.
While kbin will show you content if you open the site in a browser, that’s not a “public timeline” like Mastodon’s.
Upvotes are actually not specifically defined in Activity Pub. Kbin and Lemmy use “Likes/Favorites/Stars” on a thread/post for upvotes. Downvotes don’t exist at all in the specification so Mastodon and other platforms can’t understand them at all.