I know what you mean about the stroke patient thing.
I had (still have, actually) RSI-ish problems in my right wrist but not my left, so I started mousing with my left hand and it felt exactly the same. Years later, my day-to-day productivity has fully recovered, but I still can't play mouse-intensive games like Minesweeper without getting confused and clicking the air with my right hand when I meant to use my left.
To help with RSI from the mouse, I got a trackball. It lets me keep my hand at a comfortable position and just roll my thumb ever so slightly to move around. My wrist never needs to touch the desk, so carpal tunnel is mitigated.
You might just be ambidextrous with a strong right hand. My strong hand is the left, but besides more complex things like writing I can also do pretty much everything with my right hand without having to train.
I had (still have, actually) RSI-ish problems in my right wrist but not my left, so I started mousing with my left hand and it felt exactly the same. Years later, my day-to-day productivity has fully recovered, but I still can't play mouse-intensive games like Minesweeper without getting confused and clicking the air with my right hand when I meant to use my left.