Basically the exact meaning of the various channels and their values is vendor specific. So please consult extern sources to be sure what the values mean exactly. The channel id is part of the channel name in PRTG, followed by a ":". After the ":" PRTG states the "typical meaning of the channel", but please be carefull, not all vendors stick to the "typical meaning" but define their own meaning!
Generally each channel reported by the WMI System to the HDD Health Sensor contains information on the state of the channel (e.g.."Might fail soon") . This information is processed by the sensor and PRTG sets the sensor automatically to warning state.