The "similarsites" link you provided has added a search frame and is loading your site in that frame. If you click the "X" in the upper right corner, you're taken to your WordPress.com site. It looks like their service will help a user find other websites with content similar to your own site.
Alexa and CraftKeys are sites that provide analysis and statistics for websites on the internet. They are not copying your content, just analyzing it.
Your site is public and that means your content can be indexed and searched by Google, Bing or any other search engine along with being open to being analyzed for it's content by sites like Alexa. The only way to prevent this is to have a completely private site, but then you won't get any traffic from these searches or services.
I hope that clarifies things.