Yes you are right, however i think it is possible that you have some hardware-glitch as mention by others. If have two phone, try to check the other one, which you use for battery loading. However it should do what it supposed to do, and maybe you are the 0,01 % of worth folks which was attacked by a parcel interception an got a modified hardware, mentioned by E.S. - which is unlikely but possible. I think you have just rub of some Plastic by usage or a shortcut on your circuit or a physical or biological one like dust or hair.
However. I like the Hardware - Kill Switches. But i bought that phone cause of Linux. Since in my daily life there are so many untrustworthy Systems from Amazon, Alphabet, Microsoft, Apple - that my Friends and Family use. That its strange to have some phone too. However its in the long run the best Option. But if we can not established a free Internet, like in the old days its like only a small wall in our privacy garden. - Right know its Gold Standard.
After seeing this i thought about you have maybe Mobil Data activated. Or that some Connections through Bluetooth are still available. Or that you have a LAN-Connection through an USB-Adapter to a Computer serve you with Internet, or some Bluetooth or Mash - and you like to make some Riddle for the Community here to place this Video.
Or that you just explain and read it, but post from another device. Its possible - but i do not think so Dlonk, because i trust you. So i think your Plastic on your Kill switch have a bad Position or your Phone got Modified. - As i say, i could not verify your phone behavior cause my WLAN got lost after using my Kill switches as i mention and if i have Mobile Data on i have some 3G or 2G Message. However if i have no Internet if have the crossed double arrows on my top bar, which you do not have in your Video after activate the Killing-Switches. So your phone have some Route to Internet. I think it may be some kind of Zero Config in your WLAN/Smart Devices Configuration, on your Routers.. like this Zero Config Network Stuff enabled by Apple and some others… Check your Logs and “# route” Settings.
Edit: It could be Ipv6 Configuration too. There will be some Automation if your phone see and find a Carrier any maybe you (or some malware) forgot about trying one configuration in the past. With neighbour Solication and a route to Intert and Zero-Conf it can be that you test this and your phone still find and see this device with Bluetooth or the Modem ( i did not check the ipv6 usage on my L5.) But i know that i can use an establish connections to devices in the same “space” and with WLAN its possible if your Smart-TV have an free uplink or some ipv6 Device you do not know, that can establish a free internet connection for you. Like free WLAN in the Town.. Check IPv6 and IPv4 Firewall and Routing-Rules too!