At what point does cardio become strength training?

This question came to mind as soon as I found the rowing machine: http://www.gmshps.com/wp-content/uploads/2015/05/rowing-machine1.jpg

and my mind connected it with the seated row: http://www.bodybuilding.com/exercises/exerciseImages/sequences/45/Male/l/45_1.jpg

Both machines require you to do the same movement but one is for endurance and the other is for strength training.

So my question is, at what point does cardio become strength training?