It doesn't appear that they said the second amendment applies to the states. What they DID say was, "In any event, the Supreme Court has unambiguously held that the Constitution and Bill of Rights are in effect in the District."
In other words, the second amendment applies to the District of Columbia. Which was all the court was concerned with.
To summarize, we conclude that the Second Amendment protects an individual right to keep and bear arms. That right existed prior to the formation of the new government under the Constitution and was premised on the private use of arms for activities such as hunting and self-defense, the latter being understood as resistance to either private lawlessness or the depredations of a tyrannical government (or a threat from abroad). In addition, the right to keep and bear arms had the important and salutary civic purpose of helping to preserve the citizen militia. The civic purpose was also a political expedient for the Federalists in the First Congress as it served, in part, to placate their Antifederalist opponents. The individual right facilitated militia service by ensuring that citizens would not be barred from keeping the arms they would need when called forth for militia duty. Despite the importance of the Second Amendment’s civic purpose, however, the activities it protects are not limited to militia service, nor is an individual’s enjoyment of the right contingent upon his or her continued or intermittent enrollment in the militia.
It applies to Individuals. It protects their RKBA no matter where in the US they are, even the District of Columbia. No Federal, or mere State law, may infringe on this Right as per the Constitution.
Keep spinning Bobby. It's what you do worst...
They did have to hold that the 2A is an individual right against the Federal Government to reach their conclusion. So, it's certainly a boost for the individual rights view.
You are correct that they didn't reach the incorporation question. There was no reason for them to do so in this case.