I think his attorney laid out a good case for dismissal in the interest of justice. Hopefully the DA will agree and dismiss the charges, or at least allow him to plea to a violation instead of the proposed misdemeanor.
Another possibility: The DA is not required to tell the grand jury of any exculpatory evidence, even if it was valid evidence (however, ignorance of the law is not a valid defense), but the DA can present any information to the grand jury, including the evidence that the marine thought his permit was good in NYC, even though that would not be a valid defense. Then if the grand jury refuse to indict, the DA is off the hook - he just blames it on the grand jury.