I think the transition from a geographical distinction to a "scene" one was really a slippery one that started with the writings of Tom Johnson in the Village Voice starting around 1977 where he'd differentiate by referring to groups of composers working downtown and then referencing The Kitchen or Artists Space. I think that it started to have a stylistic meaning around '80 or '81 - still by Johnson - just because the divisions were growing clearer and the term was already circulating in the informal speech of the time so it just naturally worked its way into reviews with the knowledge that VV readers would just know.
RIP. I discovered him via Traffic and still have a copy of Alone Together.
He played nearby (Bearsville Theater) in 2015 but I was too cheap to go. Now I regret that.
I saw him with what I think was the first performance of "Derek and the Dominos" at a fundraiser in London. (Can't remember the theater but it was on The Strand.) I once had an argument with someone who knew Mason and said that couldn't be true or he would have known about it. He picked up his phone and called Mason who confirmed my story.