He said it was something to do with static electricity.
It sounds like he was confused.
What that process actually does is ensure the device is fully switched off to clear any fault.
Many modern devices never really turn off completely, especially battery powered ones. Switching them "off" just puts them into some level of standby.
If some kind of fault has caused the system to 'hang' then pressing the power off button won't necessarily stop whatever is going on, often because the system needs to be running in order to go through the shut down/standby process.
The screen might go black, but inside the processor might still be stuck in an infinite loop or some other situation which will never complete.
Removing the battery is the equivalent of removing the mains plug from the socket, but with electronic devices there may still be enough residual electricity in the internal circuits to keep the system running for a few seconds, or to keep information stored in RAM.
So keeping the power button pressed down (after removing the battery) is done to ensure any residual power has drained away and the device is fully 'off'*.
That means when the battery is replaced or the power turned back on, the device is starting from cold with the previous problem fully cleared.
(*except if the device has a real time clock (for example) in which case it may have another internal battery and some parts of the system will still continue to run)