1 - If you want to edit the max rapid rate for Z change your $112 GRBL value (Also check $122)
For carving at design machine speed (feed rate) is governed in CAM.
So if $112=3000 your Z will at max rate move 3m/min up or down. This speed will be used when the machine is moving but not cutting. The cut speed (feed rate) is set during CAM and can be anything.
Your example video consist of a gode saying:
2 - “Move down close to material” (max rate, or max rate set in CAM)
3 - “Now you are close to the material, use cutting speed now while ramping down in circles”
1 - Fixed GRBL parameter, the machine will not go any faster than this
2 - Can be specified in CAM or just use max rate (depend on CAM options)
3 - Fully controlled in CAM