On link 2 and link 3 you find some information.
You get the same note with pushing and pulling.
Some of the buttons (in different rows?) gave the same note.

right, so called "button accordion" (freely translated from the Dutch language). So, there is chromatic piano accordions and chromatic 'button'accordions. Like Glenn said, there are 2 systems.
In Dutch we call a button accordion a "pull harmonica" or "pull bag". NEVER call a squeezebox an "accordion" in Holland!

Tune played sounds like a French Musette, but I am not an expert.
In fact the name "Musette" comes from the French bagpipe, and on this field I have more expertise.

Gus

You'll also notice that some buttons go down when another is pressed, meaning they're the same note, tied to the same linkage.

Chromatic Button Accordion, in American parlance. When in doubt, see how much in and out they have to do to do a run.

in and out?
you don;t have to go in and out, the
notes are the same in each direction

wle.

Right. One of the hallmarks of most chromatic accordions is Double Action. You get the same note on the push and the pull, two identical reeds for each button. Now you can get "rythmn effects" by using the push and pull, rapid pulses etc, but you really never run out of air on a note. You just reverse direction and the same note sounds. All piano accordions are set up that way. I don't know of any single action piano setups. Most diatonic accordions are single action (are there any double action diatonics???) That would require at least two rows to get 20 notes. Not sure if that would make any sense.

I wasn't verbose enough I guess. I made the initial determination that it was a CBA by the number of rows, but I've heard of 4 row diatonics, so then I looked to see how much he was moving the bellows in and out. Mostly, not much, which told me it was a CBA.

I'll be even more verbose. Towards the beginning of the video, he was doing some amount of in and out, which confused me. Now I know that he was just trying to keep the bellows close in, in anticipation of a long unbroken run to the out site.