From what I remember when I had a wacom tablet in the 90s and 2000s, the tech was something like RFID where the active tablet would read the passive puck and stylus and get sub millimeter accuracy from triangulation. This included tilt and angle of the stylus.

The stylus pressure and buttons was a sensor on the stylus that was sensed by the tablet.

The screen or surface didn't have any sensors.

Nope. Surface Pro 1 (and 2?) used Wacom tech, had 10-point multitouch, and the stylus didn't need batteries or recharging. The induction stuff that Wacom does is pretty cool.