Why am I reading 22VDC / 69VAC when measuring between myself touching a MacBook and ground?
Unfortunately my assumptions were incorrect.
The part that defied logic to me was that the reading would still persist when the MacBook got unplugged from the charger. However the metal case around the charger plug is the culprit.
When unplugging the plug, I was touching both the computer and the charger with the same hand, leading to the wrong result.

If properly unplugged and while not touching the charger plug itself, I do not read 23VDC/69VAC. The explanations in the comments do apply in that case, thanks.
It's only leakage current being seen from the charger.