Actually, I did read that a bit wrong. The District is enjoined against enforcing § 7-2502.02(a)(4), which reads:Meaning while you may be right that Y group of people can do X, Tom can still have it right that the police will arrest Y's until it shakes out and any Y's who don't want to go through the hassle should listen to what Tom said.
A registration certificate shall not be issued for a (...) Pistol not validly registered to the current registrant in the District prior to September 24, 1976
This means registration for new pistols must be allowed. This was supposed to be the result of Heller, but DC has done their best to make that process all but impossible.
The other statute is § 22-4504(a), which reads:
No person shall carry within the District of Columbia either openly or concealed on or about their person, a pistol, or any deadly or dangerous weapon capable of being so concealed.
So, it's actually two different things. However, handguns possessed in the District are still required to be registered. The DC authorities could argue that the first provision (registration) overrides the second (non-resident carry), and they could bust people for carrying an unregistered weapon.
Bear in mind, they're going to do everything they can not to comply with this.
Of course, we could tell those Texas open-carry guys to give it a go and let them be the test case.