Jury nullification occurs when jurors choose not to convict a defendant they believe to be guilty of the offense charged, usually because they conclude that the law in question is unjust or the punishment is excessive.I am surprised that someone would defend jury nullification this way, but apparently the common definitions include the juror believing that the defendant is guilty of the crime.
I always thought that jury nullification included situations where the jury agrees that the defendant did the alleged acts, but maybe did not have the required criminal intent, or has some other valid legal argument for an acquittal.
Guilty is a legal determination, not just a factual determination. If the jury says that the defendant is not guilty, then he is not guilty.
The prosecutor may argue that if the defendant pulled the trigger, or possessed the drugs, then he is guilty. But legally, it is always more complicated than that. There has to be admissible evidence against him, a fair trial, mens rea, etc.
If a juror agreed with the law, but did not agree with how it was applied in the case and honestly voted for the defendant being not guilty, then I thought that a prosecutor might call it jury nullification. But by the above definition, I would say that it is probably not jury nullification, as the juror could have a legitimate argument for a not guilty verdict.