As he should have done. His job was to determine the facts and the law. He did so, avoiding wandering off on some bunny trail. His decision does two things:
Says that the words Citizen at Birth (language from USC 8, Section 1401) mean the same thing as Natural Born Citizen
Finds that Cruz is a citizen at birth (by virtue of USC 8, 1401)
Appeals will need to challenge these points, or assert that the Congress had no power to act under their plenary power under Article I, Section 8, U.S. Constitution. I believe that any appeal will affirm the decision and will reject any challenge to the Constitutional power of Congress on this point.