If you turned off your camera while it still had a Wi-Fi connection and then detached it from your iPhone, it will automatically reconnect when you turn it on again. You can prevent this from happening in two ways:
- Re-attach your camera to your iPhone, which will automatically disable the Wi-Fi connection. You can then detach your camera to use in standalone mode. Then when you turn off your camera, it will not reestablish a Wi-Fi connection when you turn it on again.
- Attach your camera to your iPhone and turn it on. When your iPhone has re-established a connection, go to the “Wireless Remote control” menu in the camera's Capture settings, and tap on the text that controls connecting/disconnecting Wi-Fi.