It's often used for a "trivial or minor fact" but by comparison with planetoid (something like a planet but not a planet) or cuboid (like a cube but not an actual cube) or asteroid (looks like a star but is not a star) or humanoid / android (having the form of a human or man while not actually being one), you can see what the 'correct' usage should be.

Trivial fact would perhaps be better as 'factette' or 'microfact'.

I have also heard people use it to describe a "bite sized fact". The "oid" part of the word, for some people, seems to mean "small" or "compartmentalized".

In this incorrect usage of the word, take the following sentence: "Nice little factoid!", could also be written as "Nice little nugget of info!"