The two black wires on the Touchless Switch are used to make the TS work. There is a third wire that is green and is riveted to the switch faceplate. The green wire’s only function is to ground the metal parts of the TS. Most device boxes, the thing into which all switches are mounted, are made of metal. And, the screws that attach the switch to the device box would do a fair job of grounding the switch faceplate however, some device boxes are now made of plastic.
It is a CSA/UL safety requirement that all metal parts in an electrical system be well grounded.
So… to be sure the TS faceplate will always be safe, there is a green wire which must be connected to the ground for the device box.