This is additionally confusing because different prominent platforms use different systems - eg, 1500ish is the 50th percentile on lichess (used in the blog post), but chess.com (which many streamers / online commentators use) has more like an 1100 midpoint for its ELO-approximating system, and 1500 is reasonably high there (it also varies with time control I believe). And USCF+FIDE use other systems altogether.

It's basically impossible to discuss chess ratings or changes in them without "type" information :)