Yes, let's look at the Lautenberg Amendment, shall we?

https://www.law.cornell.edu/uscode/text/18/922

(9) has been convicted in any court of a misdemeanor crime of domestic violence.

He was brought up under UCMJ Article 128. UCMJ offenses are not misdemeanours.

The UCMJ does not classify offenses as petty offenses, misdemeanors, or felonies. Whether an offense is considered within any of these classifications is a matter of other federal or state law definitions.

While the military chooses to interpret the ban in such a manner that it chooses to apply it to service members charged under the UCMJ, that policy isn't legally binding once you get out. The statute is very specific - you either have to have been convicted of a misdemeanour, or under the GCA, an act which could have been punished by a year or more.

So, if you committed assault with a firearm under the UCMJ, that is punishable by three years, and qualifies you as a prohibited possessor (unless you are tried in a Special Court-Martial, in which case the offence is limited to 1 year, and would not qualify). It qualifies because the Gun Control Act simply says convicted of an offence.

The Lautenberg Amendment, on the other hand, specifically requires a misdemeanour to apply. Article 128 is not a misdemeanour.