2:12 PM, Friday September 3rd 2021
If the endcaps of the box that the ellipses sit in are perfectly square in perspective then the cylinder will objectively be circular in that same perspective. However there can be some other perspective grid/camera lens that could make a different oval-ended cylindar look exactly like that first circular cylinder. In the same way that a lot of optical illusions like playing tricks with skewed forms that appear like boxes to the viewer and immediately collapse when you view it from a different angle.
The difference in ellipse degress (minor/major axis ratio) comes from behavior of perspective and the dimensions of the box remaining constant. So, yes that is one indication that you got it correct.
That is where I am at with my understanding anyway. I hope that answers your questions.