He's earning by upvoting posts, which is also called curating. He's regularly listed on the top curator's list - @furion created a page on his steem.li site: http://steem.li/curators .

@thecryptofiend along with help from the community created a great Steemit FAQ that goes over curation in more detail: https://steemit.com/steemit/@thecryptofiend/the-missing-faq-a-beginners-guide-to-using-steemit