Touch Sensing

Hello All,
I am using On Pin to sense touch. In years past, the touchee must be grounded for this to work, but I was able to trigger a tough just by touching the pin AND no connect to ground while the project is plugged into the laptop. If I disconnect and go battery power only, then I must also touch ground to make it work

And yes, I have checked that I am not grounded to the laptop some other way…basically standing on a wooden floor and the project is on a rubber mat.

Does anyone have a good laymen’s reference for how touch sensing works on Micro:bit?