^LOL
I'd disagree; replace "vernacular" in his sentence by the world "language" and it doesn't make sense; they know the correct "language" - ie: automobile lingo - but they don't know the correct terminology for the application, aka vocabulary.
I really don't want to start a drawn out discussion on grammar/vocabulary/language/etc. though...those get annoying to read. I'll move on.
Uhh, you started it man............vernacular doesn't mean language specifically....because language means....."language". Here is the definition from webster.
Definition of VERNACULAR(adj.)
1a : using a language or dialect native to a region or country rather than a literary, cultured, or foreign language b : of, relating to, or being a nonstandard language or dialect of a place, region, or country c : of, relating to, or being the normal spoken form of a language
2: applied to a plant or animal in the common native speech as distinguished from the Latin nomenclature of scientific classification <the vernacular name>
3: of, relating to, or characteristic of a period, place, or group; especially : of, relating to, or being the common building style of a period or place <vernacular architecture>
— vernacularly adverb
Examples of VERNACULAR
Definition of VERNACULAR(noun)
1: a vernacular language, expression, or mode of expression
2: the mode of expression of a group or class
3: a vernacular name of a plant or animal
Examples of VERNACULAR
He spoke in the vernacular of an urban teenager.
phrases that occur in the common vernacular
He can use vernacular if he wants
Definition of VOCABULARY
1: a list or collection of words or of words and phrases usually alphabetically arranged and explained or defined : lexicon
2a : a sum or stock of words employed by a language, group, individual, or work or in a field of knowledge b : a list or collection of terms or codes available for use (as in an indexing system)
3: a supply of expressive techniques or devices (as of an art form)
And you are equally right to say vocabulary.
If its not broke don't fix it. He was fine and everyone knew what he meant, but you wanted to correct him when it wasn't warranted, hence the only reason I went out of my way at 1:00 in Afghanistan to show you that you are not right....or wrong for that matter, but really didn't have to say anything.
That sir.....is an english lesson