He's going to lose. There's a relevant case I read recently (will update when I find it) that is very similar, and they said that as the victim was an intimate partner, it constituted doemstic violence, whatever the nominal charge, and was upheld as a bar to this guy's gun rights.
In the meantime, this is the applicable standard:
A "misdemeanor crime of violence," pursuant to 18 U.S.C. Â§ 921(33)(a), means an offense that:
has, as an element, the use or attempted use of physical force, or the threatened use of a deadly weapon, committed by a current or former spouse, parent, or guardian of the victim, by a person with whom the victim shares a child in common, by a person who is cohabiting with or has cohabited with the victim as a spouse, parent or guardian, or by a person similarly situated to a spouse, parent, or guardian of the victim.
As of September 30, 1996, the new law went into effect. However, the prohibition also applies to persons convicted of misdemeanor domestic violence AT ANY TIME PRIOR
to September 30, 1996. Therefore, as of the effective date, any person who has EVER
been convicted of a misdemeanor crime of domestic violence may no longer possess a firearm or ammunition.
With respect to all persons convicted, the law would NOT
apply if the conviction is defective procedurally due to representation or trial issues, such as the person's constitutional rights to counsel and/or a jury trial were not knowingly and intelligently waived. Also, the law would not apply if the conviction has been expunged, set aside, pardoned, or the person has had his or her civil rights restored and the person is not otherwise prohibited from possessing firearms or ammunition.