I think the most confusing factor here is the (potential) mental component to these injuries. I personally ruled that out as a possibility for the first five years or so just because it didn't really fit into my understanding of things that I could experience physical pain via something mental. The idea was tantamount to calling the pain artificial, which I knew was very much not the case.
The article (and others here) mention Dr. Sarno. I also read a couple of his books, and a couple more from others who think in the same basic framework. It helped. I'm certain there is/was a mental component—but I don't think Sarno et al's framework is good enough yet (don't get me wrong though—it does work for some people). Aside from results being imperfect, the fact that much of it is grounded in Freudian psychology is an obvious defect. I think they've hit on some techniques that can help, but the theory is bad (which prevents them from effectively refining the techniques).
My latest idea on what has caused all of this: I had some kind of physical injury early on (maybe tendonitis), and it eventually resolved itself. However, I developed this habit of very anxiously monitoring/testing the wrist/hand pain whenever using mouse and keyboard, which would cause the muscles to tense to the point of being painful. Unfortunately, my mind failed to distinguish between the original pain and that caused by tensing, so I continued operating under the assumption that I had some RSI, and continued vigorously worrying about it and attempting to solve it.
The only thing I can think of doing now (and which I am actively doing), is getting better at meditation so I can hopefully one day let go and not worry and tense up while using mouse/keyboard :/
It's been 10 years since then. I now have zero problems, no special exercises, no ergonomic keyboards, chairs, desks, etc. I also regularly play ARPGs like Diablo 3 and Path of Exile, which make most people with RSI cringe.
I agree that Sarno's framework is not perfect. I'm not sure I buy his explanations as to why it works, but it does work. The key is that there is a huge mental component to RSI (or, at least, to some cases of RSI) that most people don't acknowledge. The monitoring/worrying about damaging yourself does something to those muscles/tendons that builds up over time.
However, I don't agree with Sarno's view that the mind uses pain as a diversion from psychological or emotional issues. I think it uses to pain as a way to get our attention, to let us know that we need to deal with those underlying issues.