But that’s what I’m saying — iOS devices don’t just connect to random unsecured networks because they have nothing better to do. Spontaneous connections to open unsecured networks isn’t a thing; at some point, you would have told your device to connect to a “Telstra Air”, “Fon”, or whatever wireless network you find your iOS device connecting to when your Wi-Fi isn’t available.
While there’s no way on iOS to display the list of networks your device has connected to, you can reset network settings which will wipe all of the known wireless networks from your device.
From that point on, provided you’re not using iCloud Keychain to sync known Wi-Fi network passwords between devices, your iOS device will only connect to networks that you explicitly tell it to, either by entering the password if it’s a secured network, or by tapping on the network name in the list.
Given that wireless networks are remembered by name and not by some other technical identifier, if you connect to any other wireless network named “Telstra Air” or “Fon”, at any point, then yeah, whenever your own wireless network isn’t available, it will look for alternatives. And hey, presto — it will connect to your neighbour’s Wi-Fi named the same thing, even if you’ve never connected to it before, although I’d have to test if security settings play a part (i.e. will it automatically connect to an unsecured version of “Telstra Air” if the only other “Telstra Air” Wi-Fi network you’ve connected to was secured? Not sure on that one.)