That's not necessarily correct, the ram will most probably work. But since the ram in not on the list, that is an indication that ASUS has not, or did not, test that particular ram with that particular motherboard. And since the ram was not tested with that particular motherboard, ASUS therefore does not, and will not, guarantee the function of that ram with that board.
Ram that appears in a motherboards QVL has been thoroughly tested with that board and is therefore basically guaranteed to work with that board in the best way that it can. Ram that is NOT in the QVL list will most likely work provided that you are using DDR3 on a DDR3 motherboard and not trying to cram DDR4 into a DDR3 board. So, it may, or may not, work but if it does, then it will not work to the best that it can.
Sort of like putting different size tires on your automobile. Sure, the car has four tires, one on each wheel but if the tires are not from a set and are mixed, then you expose yourself to problems as the tires shaking or wobbles. Could also suffer from the car wanting to pull to one side of the road and other stuff. That is why ram comes in sets, the modules of a set are warranted and guaranteed to work their best when they are together on the mobo.