Beemaster, I may have misread the article, but, I don't think the gun was loaded. I do not recall a reference to it being loaded.
Even if it is a gun, it was from the 1700's. Not something you can load easily even if a ball and powder were in the car somewhere.
Would it even be considered a weapon if it could not be fired? From what I read, the owner considered it an antique.
As to the laws requiring guns and loads being in separate compartments, for the record, I think they are reasonable, more so for city folk.