If you are creating art, no matter if you follow another's design or not, then you are an artist....just not a designer. An artist creates beauty, they don't necessarily design that beauty.
Perhaps you should add a catagory or question...when does a quilter become a designer? Is it when they change the colors of an age-old pattern to suit themselves? Perhaps when they make up a new pattern from start to finish? (Is that even possible except with a landscape type of quilt?)
I think it's all a matter of perspective. Many oil painters think that Thomas Kincade is NOT an artist, that he uses "tricks" instead of creating art. (Don't ask me to explain, I got disgusted with that conversation and left the room after I heard that, without waiting for explanations from those talking about him) If you were to follow the same thought pattern, Jinny Beyer is just a quilter, and not an artist or designer...because she uses patterned fabrics to create with...
~shrug~ Not sure I made my point clear...and really not even sure it matters... just that in my mind, everyone that puts together pieces of fabric, batting, and binding is an artist of SOME degree...