Orthogonal does not mean unrelated. Take two vectors in the plane. Them being orthogonal means that they have a 90 degree angle between them, so if you know the direction of one of them, the direction of the other one is severely restricted to two choices. So these vectors are very much RELATED. It's just that they are related in a way that makes them maximally different in a certain sense.

So if you want to say that two things are maximally different in a certain sense, you use orthogonal. If you want to say that one thing has no influence whatsoever on what the other thing is, and the other way around, you use unrelated.

For example, if you randomly choose a point in the plane, then its x and y coordinates will be unrelated, but not orthogonal. The vectors [x 0] and [0 y] are not unrelated, but certainly orthogonal.

Of course, this distinction is easily lost.

Unrelated is more general, and less precise. Orthogonal restricts the "unrelatedness" to the specific property being discussed. It's also a very visual and intuitive word.

It's not only HN btw.