Specific Question about the DC gun case and the Supreme Court - Incorporation

Well, that’s not true as many States include the same right in their Constitutions.

From the context, I think Andrew Bird is asserting that an individual does not have a right under the federal Constitution to have a grand jury in state prosecutions.

State constitutional law may give a right to a grand jury, but if the state abolished it, that action would be constitutional under the federal constitution (subject to the due process concerns outlined by Polycarp).