An interesting article overall, but I think authenticating a user based on their IP address is probably the worst security advice I've seen. It's probably ripe for attack with ARP poisoning, IP spoofing, etc.
It only authenticates it _after_ all the WireGuard bits. So it's not really auth by IP address, but auth by wireguard key identity, from which we know your identity. There's no IP spoofing possible. And ARP isn't even in the picture for an L3 protocol.
A malicious game on my phone can't ssh to my server if I do normal authentication, but with this IP/WG authentication it can...