I've always interpreted the quote as meaning that good artists are able to recognize worthy work and imitate it, while great artists take that work and make it their own, improve upon and personalize it.

The Macintosh team "stole" the GUI from PARC, insomuch as they turned an academic experiment into a user-friendly, commercially viable product with its own refined sensibility and personality.

Samsung was a good enough artist to recognize that the iPhone was worth copying slavishly (albeit poorly), but they never turned their imitation into a distinct work unto itself.