It's not meant as an actual manual. What you're really supposed to do is comb through ad-ridden google results until you find that one 10 years old reddit thread where someone thanks a deleted comment for solving the issue you have.
This is dumb. I'm currently sitting at a computer at work. It's not my computer. It's not even my workstation at all times, who sits where depends on how the shifts work out each day. "This computer" is a more general expression which encompasses "My computer", one which is more correct in many cases and slighly less precise in the case of your computer at home.
It makes perfect sense in a world where it's common for people to use a computer they do not own. The former designation didn't. Hence the change.
And guess what? If you really care, you can rename it to whatever you want.
Yes. It's called gambler's fellacy because it leads to free blowjobs.