Here is Qingping’s response:
The method of obtaining the VOC index readings by Qingping air monitor 2 is the same as Sensirion, but the evaluation method is different.
Since the Qingping Air Monitor 2 allows the VOC readings to be switched to mg/㎥ or ppb, we have a specific evaluation standard for mg/㎥ and ppb, which aligns with this scale.
So, in other words, Qingping’s index uses ‘absolute’ readings and follows a Chinese standard (found here: https://www.mee.gov.cn/image20010518/5295.pdf). I assume the german guide values are those listed here: https://static.dgnb.de/fileadmin/dgnb-system/en/buildings/new-construction/criteria/04_SOC1.2_Indoor-air-quality.pdf