What are you taking about? Only 3 judges on the 9th said said he didn't have a case. None of the dissenting judges on the 9th expressed that opinion.
Here it is again. Tell me what I'm missing:
The District Court in Washington State found that Mai did not have a case. Mai appealed to the Ninth Circuit. On 11 March, 2020, in a unanimous decision from the three-judge panel, the Ninth Circuit upheld the District Court decision.
Mai asked for an en banc review of his case. En banc reviews of Second Amendment cases seem to be routine for the Ninth Circuit, when the cases favor protecting Second Amendment rights.
This case, which had already ruled against Second Amendment protections, was, unsurprisingly, not granted an en banc review.
So because he was committed when 17, and the record was cleared by Washington state, the Court will not let him off the law, 18 U.S.C. § 922(g)(4), which forbids Mai from purchasing or possessing a firearm. So he cannot own a firearm.
The courts said "No firearm for you".