Theft is theft whether or not it is so called by our particular laws. Had anyone suggested that we seek a remedy for these thefts in the law then, and only then the question of what the law thinks would be relevant. As we haven't, the legal definitions are irrelevant.
The basic question is this: has Magic Makers taken someone else's property?
This is easily answered if we have a clear view of what property is. I am partial to John Locke's:
If my hands are my own then a fortiori my mind is my own. If the products of the labor of my hands mine, then the products of the labor of my mind are -- a fortiori -- mine. Paul Harris, John Kennedy, Finn Jon have all clearly invested their labor into ideas that have been appropriated -- without any compensation -- by M*gic M*kers....every man has a property in his own person: this nobody has an right to but himself. The labour of his body, and the work of his hands, we may say, are properly his. Whatsoever then he removes out of the state that nature hath provided, and left it in, he hath mixed his labour with, and joined to it something that is his own, and thereby makes it his property. (Two Treatises of Government II.V.25)
It was their labor. It was their property. It was taken from them. That, friends, is theft.
Best,
N.