I'm not sure there is case law to support that argument. I am not sure that there isn't case law to support it either. Even if there is case law to support it, the circumstances in which the case law is helpful are somewhat likely to be more expensive than licensing other music more explicitly providing more conventional copyright permissions. For example, assuming the premise that the copyright belongs to the user in a case where two different users enter the same (or even similar) parameters then one of their compositions is probably copyright infringing on the other author -- or both are on a third even earlier author who entered the same or similar parameters.

Again I am not a lawyer though it doesn't prevent me from thinking along the lines I have observed laywers thinking.