It must be a myth that only the POTUS is authorized to call up National Guard, in the District of Columbia.
Others can request it, of the president, but these local underlings directly discussing their own “contacts with the NG” would seem a non-starter.
This avenue would just be giving your 'contacts' a heads up. Not surprising that the Capitol Police would know their counterparts in DC Guard. There are AD serving with the Guard who run day to day operations.