I would agree that the record should be as accurate as possible, Mr. Davis. I have not used the registry myself, so I can only offer suggestions.
This message is found at the WWII Memorial web site:
For General Information: Write: National World War II Memorial 2300 Clarendon Boulevard, Suite 501 Arlington, Virginia 22201
Perhaps they could tell one how to go about getting an erroneous entry corrected.
If you don't have success in that manner, you could probably register Private Ferguson yourself (I have seen any number of multiple listings for individuals), and note in your listing that you are his stepfather, and that his listing as attributed to the Archives is incorrect. This would seem to be a last resort, but might be better than leaving the error unaddressed.