Apple in iOS 11 decided that when you tap the Wi-Fi or Bluetooth buttons in Control Center, the system now will disconnect you from any devices or networks you are currently on but no longer truly switches Wi-Fi or Bluetooth off.
This means that even though you thought you switched them off, they remain active for things like AirDrop, AirPlay, Continuity, Hotspot, Location services and devices such as the Apple Watch and Pencil.
An Apple tech support note says this is so you can continue to use those “important features.”"Important". Oooooh kaaaay. Pay no attention to that man behind the curtain selling location-based advertising.