Body Sensor Permission? What all kinds of information could it get of our body?

How is the Body Sensor Permission utilized by the apps? \ I'm aware that it uses a hall and proximity sensor to detect human presence. I want to know how exactly it detects specific people. I'm talking of the smart lock: On-Body Detection. It used to be fairly inaccurate but the hall and proximity sensors cannot distinguish between bodies (i think, correct me if I'm wrong) \ So is there something I'm missing? Can it read my ("vital signs") respiration rate, heart rate or body temperature (as it says on the screenshot)? I'm particularly interested because Google has it and Google has made it just for itself!? I've not seen any app request for this permission !. ! Googling shows body sensor is used to detect physical activities but it's not. The dedicated physical activity sensor is used for that.