Tesla doesn't seem to actually sense hands on wheel. They sense torque on the steering wheel.[1] Mercedes seems to have capacitative touch sensing, although customers complaining about it aren't quite sure.[2]
Tesla doesn't take the absence of hands too seriously. "I'm driving down the highway at 55, and I'm not looking, and I have no hands on the wheel".[3] Hands off driving in New York City traffic.[4] "I managed to go 50 miles without a single nag"[5]
Apparently Tesla does have only one camera on currently shipping products. They must be trying to do stereo from motion. There are rumors of a revision to the Model S with multiple cameras.[5]
This is not correct.
https://www.youtube.com/watch?v=Kv9JYqhFV-M