First, it says "less than $5,000" which I would expect to be "*much* less than $5,000" for the vast majority.
But most importantly, you claim that this is what artists get for "work they did last year" which I also don't expect to be true in the majority of cases. This income is most likely usually from continuously producing new music, not "residual income whilst you do nothing else for the rest of the delivery platforms life".
I wasn't able to find more detailed numbers, but I would expect income to be more driven by recent releases than "some song I wrote 10 years ago". Which means that of the small proportion of artists who even get any money at all, 90% get very little, including those that work very hard to produce new interesting music. Of course, without more detail (how many artists, how many new releases, the actual income distribution, etc.) it's impossible to really interpret that statement in any meaningful way, but I'm pretty sure that your interpretation of "getting $5,000 whilst you do nothing" is not the most appropriate.