"Argumentative" is a legal term that describes the nature of evidence given within a court case, and is used to describe something that is vague or ambiguous in its definiteness, i.e. that it lacks clarity.
If a piece of evidence is determined to be argumentative, it is not considered to be a valid fact.
Argumentative evidence is not considered fact, but rather tainted evidence that has to be dismissed because it cannot be proven.
A statement that is determined to be argumentative will have been brought up by one side, either the plaintiff or the defendant, and then objected to by the other side.