Hm, any details on that "VNC" functionality? Is it iPad only, or iOS too? Was the approval request a system pop up? Did it open a named application? Did you see what they did on the screen when they were on it? Has this been written about anywhere?
It's similar to FaceTime screen sharing, the support employee can only see a video feed of your screen but can't directly interact with it.
https://support.apple.com/en-us/HT205644
supposedly however switch control works to control other devices on the same wifi network. perhaps there's a vpn trick in the support side to leverage it over the internet at large.