It counts because the adapter slot cannot be used for something else.
I don't understand this objection. I mean, sure, if you put an audio block in a slot for the headphone jack, it can't be used for something else, but let's say they omitted a slot and just put a fixed-into-the-case headphone jack there. I assume that you wouldn't be happier with that.
I could maybe understand it if normally a headphone jack on a laptop went somewhere other than where the slots would be, but on my Thinkpad, it's where the slots are on a Framework laptop.
They just give you the option to have or not have a headphones jack.