Well, the part you saying the article refers just to placement but not absolute numbers is something you made up.
The article in fact is saying both things, that PS4/XBO are slowing down because old age (no mention of Switch eating sales), and that the lack of competition is benefiting Switch (the article specifically says Switch received a "potential boost in sales" just after saying it was because "a reflection (causality) of the competition feeling a bit long-in-the-tooth".
In conclusion, the article is saying PS4+XBO were not affected by Switch itself but by themselves (because they're old), but Switch was indeed benefited (boosting sales) because of PS4/XBO going down this year.
"POTENTIAL boost in sales"
That means they dont know if it's up or not, just that it outsold the others.
When the herd loses its way, the shepard must kill the bull that leads them astray.