Looks like a pretty spammy site. Sometimes a spam site can rank for a time using black hat tactics, but is eventually discovered and taken down. Rankings also can fluctuate naturally for many reasons-- SEOs usually see a "honeymoon period" for new pages, where they rank really highly when they are first published, before dropping in rankings after Google sees how the page performs in the SERPs.

How to Use Tumblr for SEO and Social Media Marketing
9/18/2013 Many people overlook Tumblr, but it has tremendous potential for SEO and social media marketing. I myself was slow to adopt it as a social media platform, but once I started using it I became hooked by its power and simplicity. Hopefully by the end of this post, you'll feel the same.