The Electronic Frontier Foundation warns about this in an article, iOS 11’s Misleading “Off-ish” Setting for Bluetooth and Wi-Fi is Bad for User Security, regarding this issue. They note that
When a phone is designed to behave in a way other than what the UI suggests, it results in both security and privacy problems. A user has no visual or textual clues to understand the device's behavior, which can result in a loss of trust in operating system designers to faithfully communicate what’s going on.In gets worse.
The Wi-Fi will turn back full-on if you drive or walk to a new location. And both Wi-Fi and Bluetooth will turn back on at 5:00 AM. This is not clearly explained to users, nor left to them to choose, which makes security-aware users vulnerable as well.Wifi and Bluetooth also reactivate when you reboot your phone.
Why did Apple build iOS 11 this way? Because Apple decided that it would be better for them -- make their device interworkings seem better -- than it would be to honor the "no" implied by the controls in the Notification Center.
This isn't the only thing that sucks about iOS 11, but it may be one of the more troubling ones.