It took me some time to understand the difference between Linked References and Related Posts.
Linked References are backlinks. In a topic, the Linked References section will list all other topics that have internal links to it.
Related Posts section in a topic lists all other topics that share the same tag(s) with it.
The neat stuff is, if a topic has already appeared in the Linked References section, it will not appear again in the Related Posts section.
I suggest you add the information about Related Posts in the Exploring the features of Simply Jekyll.
It took me some time to understand the difference between Linked References and Related Posts.