Apple being more clear on how iOS 11 handles Wi-Fi
With iOS 11, Apple made an unusual decision in how Wi-Fi and Bluetooth will toggle in its control center.
How it works: Turning off Wi-Fi or Bluetooth there doesn't actually turn off those radios, but instead just disconnects from the current and other nearby networks.That allows Wi-Fi and Bluetooth to remain available for a number of other uses, including AirDrop and AirPlay.
Yes, but: It also runs counter to what many people expect the button to do. So, with the latest update to iOS 11, Apple decided to make things a bit more clear. The button still works the same way, but when you press it, Apple pops up a dialog box (see above) explaining that the "off" button isn't really off.
Quick take: If you really want to turn off Wi-Fi or Bluetooth, you have to go to the settings menu.