Have Watch OS 4 GM on my watch. If I turn off Wifi, and Bluetooth on my iPhone (with iOS 11 GM) my watch still shows the iPhone icon (not the cloud icon) and I can still launch all apps and get data. Also when wifi is on on the iPhone in this area it connects to a corporate net work that watch can not access so i do not think the watch is connecting over wifi. If i put my iPhone in airplane mode then the watch shows its disconnected and no apps can get data.\
Update: Ah found it. Its a control center bug! Clicking the Bluetooth icon in control center shows it turning Bluetooth on and off, but its not. if i go into settings Bluetooth it shows its on.
So the bug is control center Bluetooth icon does not turn off Bluetooth