I think that the article is badly worded. It sounds like the person in question was TRANSPORTING a firearm rather than CARRYING one (openly or concealed).
Maryland law is extremely weird about transporting firearms.
You may only transport a firearm to or from a firing range, gunsmith or dealer; or from one another residence or place of business (yours) to another (yours).
You can circumvent this by becoming a “designated collector”, whereby you can transport firearms to and from a “private showing”.