This rule has a very easy explanation. Even if the information following your link is correct and true, the human eye is capable to see in focus only limited portion of the whole picture. So in order to draw a cylinder, one would look at it in a way, that the object (in our case ellipse) is in the middle of our sight. And in that case the rule with minor axis is 100% valid. To draw an ellipse on the other side of the cylinder one would again move eyes to see it clearly. And the rule will work again. So in fact people, when they create a picture, they fake the perspective. And only if you follow strictly mathematical approach you would get that confusing situation. And that also happens if you create mathematically correct drawing with a very wide angle of view (bigger that 30 degrees), which human eye is not even capable to catch. I hope that explanation was clear enough.