In a over taking situation the vessel beening over taken has the right of way. IIRC, it has been a long time since I raced sailboats. And of course there is always constrained by draft.
In heavy fog the container vessel should have reduced power to steerage only. 15 kts in heavy fog is crazy. I image then DG was at steerage speed and unable to react when the fast moving container vessel appeared out of the fog.
Now, I can admit that there is plenty the the container ship could have been doing that would have put them in the wrong or contributory. In either case, the Navy will come down on the Officer on Deck and the Captain as at fault. Such a thing cannot be allowed to occur.