If the "theft" from this quote counts as IP violation then all new inventions and creations become illegal and all progress would cease. I don't think that kind of outlook makes sense.
The stealing part doesn't refer to directly copying ideas (I mean what great artist would do that?), more how good artists instead are able to use other works as inspiration, "make it their own" and put their spin on it.
All great artists directly copy ideas. That is exactly what the statement implies. The point is that your own style will manifest as a mishmash of other people's ideas and this itself will constitute a new style. New ideas are just combinations of old ideas
The way I always understood it is that good artists put their spin on it.
Great artists realize perfection when they see it and just copy it, without trying to “improve” it, usually from lesser known, less successful artists so they get away with it.