Sounds like my Dh...he can talk a little about anything. And if he can't, he fakes it and I always totally believe him b/c he sounds like he knows what he's talking about...until he starts laughing!
I saw a post at another board where the kid didn't do well on vocabulary on a Standardized test b/c he didn't know words such as cafeteria, referee, etc. The mother said these were "public school" words. My friend and I have discussed whether or not HSing puts DC at a disadvantage for standard tests. It sounds like that certainly isn't the case with your DS!
