I think the reveal button is counted as an upvote for the book because it supposedly discovered my taste and it was based on th books I revealed, but not bookmarked.

That makes sense. "I read some and wanted to read more" is a useful metric like an upvote (it doesn't have to mean "I know I like this" to be useful).

If that is true, it's bad design. The site definitely needs a dislike button too, while we're at it...