I've seen this at some local games too, honestly I think the vernacular of poker lingo changes over time, in the same way English or other languages do.
'The nuts' historically has referred to the best hand, but more and more I hear it being re-calibrated in different ways, 'the nut flush' when a boat is possible also coincides and contributes to this as well.
The delineation that a straight flush is a different class of hand, straight vs flush as classes of hands. With a board of 3 possible straights, the nut straight would be self evident, but you wouldn't think to lump in the discussion of flushes while talking about .. idk 'missing a bet on the turn to protect the straight with the second best straight is crazy' - the guy talking is discussing a class of hand, be it the straights... referencing a large bet designed to make it un-palatable to call chasing a flush.
The ambiguous nature of being both a straight and a flush, you currently wouldn't think to lump a straight flush in with a straight right? following that same logic you wouldn't lump it in with a flush, hence The Nut Flush.
I don't know, maybe I'm "Inebriated with the Exuberance of his own verbosity"
I'll sit down now