Thanks for writing this, Sam McKenzie Jr.. In my experience, and note that means anecdotal, the “downlow” seemed to be a word used a lot on online dating/hookup sites for gay men, if only in my Toronto-centric experience. I only ever saw Black men using the term (which doesn't mean others didn't, but I didn’t see that).
And I have had many hot encounters with black men from that period who explicitly told me they were on the DL, always meaning they were with a girlfriend. So while it is a label, some words take on new meanings, some become associated with a tribe of people, some become appropriated by a culture, and some are geocentric.
To me at least, whenever I hear someone say, “on the downlow” I can’t help but recall some very hot sexual encounters. :-)