I saw in another comment that it's because of a last minute change for Lemmy compatibility. Apparently, /kbin originally used boosts as its upvote system, but this was changed so that kbin/Lemmy would communicate upvotes in the same way. Some of the /kbin interface is still set up to use boosts instead of upvotes. Since it doesn't break anything ~~other than hearts~~ fixing it is probably a low priority for now.