Grasping force control using Servo? (Tactile Sensing)

For a Robot hand gripper with Servo motor,

Is it possible to do Grasp force control using tactile sensor?

What does varying grasp force actually? is that a speed or torque variation in the motor?
(Like, holding a plastic cup softly, and holding a heavy objects hardly)

I'm not clear with that concept.

Or can Someone explain How it is being done and What kind of motor is used in the attached video link?

Thank you.

A tactile sensor implies that the program measures how hard the fingers are pressing on an object rather than by measuring speed, torque, current etc

Search for force sensitive sensors for examples of such devices. Judging by the video, each finger of the device had a matrix of such sensors which may be excessive for your needs