IMHO this is not correct and should be avoided since it can easily lead to misunderstandings. A spherical mirror does not have an optical axis. This is the reason why the collimation of slow mirrors is uncritical, their shape is almost a sphere. The eyepiece is mounted in the focuser. This is the weakest point in collimation, since we just have to assume that the optical axis of the eyepiece lies in the center of the draw tube, and is parallel to its path of travel.
Possible errors are an excessive play between the draw tube and the eyepiece.
This can lead to a lateral displacement of the optical axis of the eyepiece relative to the center of the draw tube. Another possible error is a 'wobble' along the path of travel, this occurs especially with rotational focusers. Usually the errors described above are too small to notice, but beware of excessive play between the draw tube and the eyepiece. Another point to keep in mind is sagging. A fully extended focuser with an heavy weight at it's end is bound to sag.