I can't answer about the size of the container in this particular case, but I learned something about shipping containers after the Baltimore bridge incident. Since the smallest commonly available unit is the 20 foot container, ships are measured by how many TEUs or "Twenty-foot Equivalent Units" they can carry. A lot of companies use 40 foot containers, so when you hear on the news about a ship carrying 1000 containers, it probably has far fewer individual containers and the reporter was just referring to the number of TEUs that the ship was rated for.