I imagine his workflow consists of a mobile device (that stays awake without user input) is plugged in to the dev machine which is running scrcpy. The scrcpy screen is then on the dev machine screen next to the editor so that code can be deployed/hot-reloaded/applied to the device as it changes. The emulator is too slow, and Jetpack Compose previews do not handle complex situations well, so a device is always the most preferred method.

This has at least been my way of developing for Android over the years.