The tilt detector is part of the BMA423 accelerometer that sends a notification to the sensor hal (/dev/m_tilt_misc -> /vendor/lib/hw/sensors.mt6739.so) if the tilt gesture was detected.
There are also some settings that can be adjusted (like the axis) to further increase or decrease the detection sensitivity.
Edit:
For the Rollme S08 the wrist gesture detection was a problem with the axis mapping, they probably turned the mainboard around due to the new IP68 based design.