The description I offered was that stated by DPR
https://www.dpreview.com/articles/6717086661/sony-a9-iii-image-quality-dynamic-range-analysis . Looking around at other reviews, most don't go into detail. DPR's take makes the most sense and the article quoting the Sony marketing guy has gone through two translations, so hard to call.
EDIT. An A/D converter at each pixel would not be helpful in that any A/D converter has finite (and typically fixed) conversion time. In order to change shutter speed, there has to be a mechanism to move the sensor charge very quickly to a place where it can be stored for conversion, so the split pixel description is the most logical.