I think there is a difference between turning it off and putting it on standby. Standyby looks like you just click the button on the side once. To turn it off completely you need to press the button for about 5 seconds until you hear it shut down.
There is a difference true. But there is a bug with in the boot and firmware that causes it not to go off after the selecting power off when holding in the power button.
I have been using my quest 2 for a year and half, and it will restart at times after full power off. It happens every so often.