This is from the various services trying to talk to each other in ways they weren't originally designed to do, really. Our "upvote" is a mastodon "favorite" (like) while our "boost" is functionally a retweet/reblog. Kbin tries to bridge the gap between threaded content and microblogging, and it gets about 90% of the way there; all it really needs to do is change it so that upvotes are the ones that contribute to reputation instead of boosts, which are functionally useless outside a fully microblog-style environment.
There's definitely room for improvement, but I like what I see so far and don't have a problem learning a new paradigm. I'm sure that as the platform matures things will become more consistent.
From what I can see the upvote / downvote both work as you'd expect now (as in upvoting curates content). There was apparently a period of time where 'boost' was the upvote mechanic but that's been changed
I've read it's a work in progress and may be changed at some point to be consistent across the Fediverse. Poor guy is slammed with feature requests and bug reports with Kbin.
Boost is like retweeting something, you can have followers in the fediverse. Boosting makes something more visible to everyone, so you upvote/downvote things you personally like/dislike and boost things you think your followers/everyone would like
Think of this place as a cross between email, Twitter and reddit. All communities can interact with each other and are independent