[Fundamentally Fair]

Understand.

More info:

DoD Ethics Counselor's Desk Book, October 2015

Off-installation political events. All members of the Armed Forces are prohibited from wearing military uniforms at political campaign or elections events. This prohibition is not applicable to the joint color guards at the opening ceremonies of national political conventions

Further

Members of the Armed Forces also includes retirees and members of the Reserve Components not on active duty including, for section 4.3, members of the National Guard even when in non-Federal status.

[Echo4C]

Yes, but the section that specifically says what members of the armed services are NOT allowed to do, begins:

Prohibited political activities (Section 4.1.2). A member of the Armed Forces on active duty shall not:

1. Participate in partisan political fundraising activities, rallies, conventions, management of campaigns, or debates. The prohibition is broad and does not depend on whether a member is in uniform or even whether an inference of official endorsement can be drawn;

Please show me, specifically, where it says what reservists are not allowed to do, and what the applicable punishment is. There's a reason this guy wasn't busted in rank or anything (though I guarantee his chain of command probably said "please don't do that").