Okay, I learned art very organically (it took me a while to even understand what this question meant) so forgive me if the ensuing explanation doesn't make sense, but...
...I think all of those things are true. ^^; Like, they're all correct in their own way.
The way I imagine it is: you are standing in front of an ocean sunset. I guess there's also a table with you.
For the first two statements from "perspective made easy", imagine you're standing in front of the table and you sit down. The horizon where the sunset is will "move" under the table; that's where you'll be able to see it. If you stand up, you will again be able to see the sunset over the table. Of course, the sunset didn't actually move, it just appears to because you changed your perspective.
For the second two statements from this Youtube guy, imagine you are looking at the sunset, and then you tilt your head and look down. Where is the horizon in comparison to your new field of vision? It "moved" up.
In the same way, if you tilt your head upwards, the horizon will "move" down. Again, the sunset didn't actually move, it just appears to because you changed your perspective.
I hope this helps?