It has something to do with several things. As far as I know, as I'm also new. But at least with the following aspects:

• Author rewards make up a percentage of the total. (So what is on the bottom of the page, is only a part of what the author makes.
• The rest of the upvote goes to curation - in short, the sooner you upvote someone, the higher your percentage of what that post makes. And also the higher your upvote, the higher your curation reward is.
• Some $ means steemdollar, others mean USdollar. This I find very confusing. And I don't know why or how or when. But it might also have to do with this.

so far my knowledge, wish I could help you more...