The must just be monitoring the temp/humidy to determine when the load is done. A simple idea, but one that didn’t occur to me.
I put an Aqara temp/humidity sensor (Zigbee based) in my dryer and ran a load. I saw that the humidity started high, the temperature started to rise, and the relative humidity started to rapidly fall. When the load was done, the temperature was approximately 122°f (low heat setting on dryer) and the relative humidity was about 14%. That’s not particularly dry from an absolute level, but with more data there must be algorithm to discovered.