Well, hapax, that is a pretty good try, but I think you are missing a few key points: let me show you how it REALLY works. Here, listen up...
Mansplaining comes in two varieties. First, there is the professorial type. The cool, competent guy who is articulate and experienced. I was actually going to explain this with a lot more theoretical baggage, describing the roles of subject and object, and the role of constructivism versus received knowledge in the formulation of knowledge, and how this all relates to gender differences. And the theoretical question is fascinating, but the best way to explain it is to bring up some cliches. The best cliche is how many female college students get crushes on their male professors. Yes, women are attracted, romantically and otherwise, to men who are intelligent, authoritative, and able to express themselves. So this is the Class 1 Mansplainer: the man who is an authority, or who can at least pass for one. Whether the Class 1 Mansplainer actually is imparting information that is useful, and whether he is doing it in a respectful, non-condescending manner, varies. Sometimes a bit of condescending is needed. While the Mansplainer Class 1 might be talking to a woman with ten years of IT experience, he doesn't know that, and he must assume the Least Common Denominator, which involves explaining things like you can't download RAM.
Men observe this interaction, and hoping to impress women, they try to copy the success of the Mansplainer Class 1. Unlike the Class 1s, however, these men are not successful. They do not manage to cultivate the combination of authority, sensitivity, urbanity and articulation that the Mansplainer Class 1 uses to impress women. Many times, they do not actually understand the subject they wish to explain as well as they should. Even more times, they don't understand the social skills, or have the communication skills, needed to explain something properly. These men typically bore, annoy or disturb women. These men don't usually even reach the level of condescension. And these teeming masses make up the Mansplainer, Class 2.
One of the things that Hapax says above is that society "rewards" men for knowing things and demonstrating their knowledge. Again, I could discuss the theoretical issues of hard and soft social power, etcetera. But instead, I will just use concrete example, directed towards the reader: how many times have YOU seen a man without obvious social status, without social skills, and without an actual knowledge of the subject, rewarded socially, (by men or women), for holding forth on Linux\Car Repair\Politics\The Moons of Jupiter. In my experience, this isn't reward-gaining behavior.
So there are two separate classes of Mansplainers: one the professorial, articulate type with actual social status, who DOES manage to impress women with his knowledge. The other type, the low-social class, low-social skill rambler who manages to annoy women with his useless information. And unlike other classes, where the two seem to grade into each other, The Mansplainers are quite distinct, someone is either very obviously a Mansplainer, Class 1 or a Mansplainer, Class 2.