Indeed, most of the world doesn't have iPhone.
And yet these metrics literally optimize for Reddit's 109 Javascript files to render a page of text with images in 2.4 seconds. And they call it fast.
However you slice, dice, or interpret these metrcis, none of these shenanigans make it fast.
What these metrics and "75p" show is that modern web sucks for everyone, and they have to pretend that 2.4s to render a page is fast because everyone is even slower.
Or, to put in context: Reddit's servers serve that page in under 200 milliseconds. There's literally no justification in the world that make it ok to say "2.4 seconds to render that on screen is fast". None.