First, the Sheriff has to manage the resources he is GIVEN by the commissioners (and to a degree the state). It's a function of tax dollars allocated to his department. He can only request additional money to hire new officers and purchase more equipment.
Second, recognize that St. Mary's county is fairly large geographically, It's long, Charlotte Hall to Pt. Lookout. There are not many roads connecting the Patuxent and Potomac Corridors as MDOT likes to label them. So while the population is not large, the area they have to cover is a challenge. Back to the first point, funding and staffing is usually tied to population (taxpayers).
Third, you cannot staff to the unexpected demand level. You staff to the normal or average demand. That's why for all emergency services surrounding communities set up mutual assistance programs. Nobody staffs to handle the unexpected surge in demand, not even major cities, they have to rely on the state, federal and other agencies for assistance in a crisis.
To me this is a none story, to me it comes off as a political attack, a political foe jumping on a call to create a strawman issue.