I understand that the Apple Watch needs a connection to an iPhone for most of its features to work, but am curious if Bluetooth can be turned off on the Apple Watch. Does the Apple Watch provide an option to disable Bluetooth?
Apparently Apple Watch has Airplane Mode, which turns off both Bluetooth and Wi-Fi.
[To] Turn on Airplane Mode. Swipe up on the watch face, swipe to the Settings glance, then tap the Airplane Mode button. The Connected status at the top of the screen changes to Disconnected. Or open the Settings app settings icon, then tap Airplane Mode. When Airplane Mode is on, you’ll see [Airplane mode icon] at the top of the screen.
Source: Apple Watch User Guide.