Is SingleLiveEvent actually part of the Android Architecture Components Library?

Looking at Live data and its Parent/Children inheritance there is no such thing as SingleLiveData. Reading link provided by @Raghu, I find statement:

The SingleLiveEvent class was created for a sample as a solution that worked for that particular scenario. It is a LiveData that will only send an update once.

So to answer your questions:

Is SingleLiveData is actually part of the Android Architecture Components?

No, it is not!

Is it a good idea to use it?

This depends on many factors. Since I haven't used it I will give general idea. Using classes that you find in demo app or other way might not be guaranteed to be updated or bug-fixed. So if you understand the class so well that you can fix any bug you might find, and if it fits your need, then use it.

But generally I would avoid that if I can find something that is well maintained and does the same job.

Since from skimming the article I get impression he is trying to make some sort of observer pattern, I will suggest you check out rxjava

Is SingleLiveEvent actually part of the Android Architecture Components Library?

No, and it won't be: https://issuetracker.google.com/issues/122413110. Basically, the official answer is "Yes, regular livedata wasn't enough, so we introduced it in our examples but it's too hacky to be in the library".