The difference between MongoDB Instance set up on a "MongoDB" single-click app vs a "MEAN" single click app

Yesterday I ran into this problem: http://stackoverflow.com/questions/30822370/authentication-always-failing-when-connecting-to-mongodb

I was confident I did everything right, but alas, had no luck. The MongoDB instance I was using in this case was an instance of MongoDB set up from the single-click-install app for Ubuntu 14.04.

After having no luck, I decided to install the MeanStack single click application. It worked out of the box so I figured I could just dissect it, see what it was doing, and what I was doing wrong. To my surprise though, I couldn’t find what I was doing wrong at all in terms of how I had set up my database query. I just popped in my own app, completely replacing the MEAN app provided with my own, and it worked perfectly with that MongoDB instance.

So this leaves the instance of MongoDB as the only difference. Something about the MongoDB set up with the “MongoDB” app, meant a query that would work in the Mean Stack" app didn’t work there. Surely, I must have missed something I was supposed to do in the MongoDB app that prevented any of my authentication-related queries from working.

So what are the differences between the two instances of MongoDB which would cause one to work while the other didn’t? (In this case, the MEAN stack app allowed me to plugin and go straight away, while the MongoDB app didn’t…)