The legislative body has the power to change the law. It's like you don't know the basics. The man is referencing the only one with the power to take away a non-justiciable law is the body that created the law. The question is can the judge make a determination as to who or what constitutes a terrorist organization? The law is written for the Executive to make that determination, not a judge.
So, this questions whether the ruling is itself legal and provides a pathway to appeal. As a coequal branch of government they continue what they are doing.... It is interesting to see where this will end up. Will the SCOTUS rule that the President, per the law, has the ability to say that this organization is an entity that "threatens invasion or predatory incursion", or will it rule that the law does not allow a terrorist organization to be considered to be an entity that "threatens invasion or predatory incursion"?