Distinct grammars within the same language, or diglossia?

[pauamma]

Reading https://allthingslinguistic.com/post/186085188112 , I came across

What kind of grammatical features does the language have?
Sentence structure is the same as English in some contexts whereas in others it strays away making the grammar fairly difficult to describe.

and now I'm wondering: is it really distinct grammars within NZSL, or something closer to diglossia, perhaps with Signed Exact English or a similar scheme?