I don't know it's fair to assume quality means theoretical quality over perceptual quality in this context. They took the time to make sure perceptual quality was quantitatively consistent, so they get a pass in my books.
I'd be angry, however, if they used the word "lossless", as that implies no _information_ is lost.
You're also overlooking the fact that they did some relatively interesting things to notice when someone posts a PNG-of-something-that-could-be-a-JPEG, and can then use a lossy image instead of the larger PNG.
Read the article. Short answer: no, while your image content breakdowns are accurate it's not actually that simple in practice as things like screenshots are pngs.
They've also got to handle photos with borders, screenshots, and such, which may or may not work better as PNGs. And anyhow, why wouldn't they want to handle un-photo-like photos and un-logo-like logos optimally too?
You misread the article. Setting the JPEG quality is their starting point. He then goes on to describe reducing size from that starting point without further quality loss.
Granted, initial reading of the title might lead you to assume he means "from upload quality", but I don't think it's intentionally misleading.
proceeds to explain how they set JPEG quality to 80-85%