You are absolutely correct.
The 8" naval gun was a product of the 1922 Washington Naval treaty, who limited cruisers to 10,000 tons and gun mounts to a range of 6" to 8".
Three classes of American cruisers had some type of an 8" 55 caliber rifled gun mount.
Other navies had them as well, and the 8 inch gun was also a popular caliber for coastal anti-ship gun batteries for a good chunk of the 20th century.
The current 8 inch gun is commonly referred to as a 230mm gun, and no US Navy ship has one to my knowledge.
Translation:
If they are 8" naval gun shells, and the reporter didnt mess that up too, they are probably pretty old. In modern navies the 8" was replaced by the 230MM.
An additional note: recent battleships on active duty (early ninties) used 16" shells manufactured in the 1930's. These things have a very long shelf life.