Thanks for the update @amarinelli
Thank you @markkus and @jarey for your replies. I did what you suggested about re-installation and the problem persisted. I then discovered something...
...the installation manual may be outdated. The file in question on Step 7 is mongod.conf instead of mongodb.conf.
Step 7 Corrected.png
Can @psychobunny or whoever in charge of the Doc double check this and make the proper correction?
Latest version of NodeBB doesn't require this dep anymore, so maybe try pulling the latest master?