How did you generate the “Possible related posts”?
It’s really simple. Automatic even.
In your WordPress.com dashboard, choose “Design” and then “Extras”
Then you will see two boxes you can check, or not:
By making sure you have the second box unchecked, you automatically generate possibly related links. And your posts are eligible to be included in the possibly related links in other WordPress.com blogs.
It’s that easy.