If I use freely provided software to create a graph, then if copyright applies at all, how can it possibly apply except to say that the graph is mine?
But then the counter argument perhaps becomes: If an artist or draftsman says he will draw graphs to your specifications for free, then if copyright applies at all, how can it possibly apply except to say that the graph is his?
What a conundrum! It's almost as if monopolies on reproduction aren't well suited to the realities of non-physical works...
Perhaps it could be argued that a graph of a certain relation of values is a "performance" of the natural facts of the statistics and mathematics involved. That way, copyright would apply, just as it does when an orchestra records music itself in the public domain.
But the orchestra's copyright is only on works that they actually record. This claim seems to be asserted on all possible displays the software is able to produce, which would be overreaching indeed. In fact, I can't imagine how their claims could reach further.