The 'normal' potentiometer is the https://www.adafruit.com/product/562
This was not included in my photos.
there is only potentiometer on there, the black wheel.
It indeed could be not 10k or linear. This is something I just read about after your and LTolledo's comment.
The "flat" potentiometer has 5 pins. See photo.
Unfortunately I can not see a part number on it or find it through the company's website or part maker's website...
I guess it's not linear since it's working with audio and increasing audio volume. (or is that too fast of a conclusion?)
Searching on the various numbers on the board with potentiometer does not bring me anywhere useful unfortunately.
Are there any specifc forums or manuals I could dive in to in order to get the part number and thus datasheet?