I’m crossing my fingers that during the handshake they aren’t passing which IP address they’re sending/receiving from. I can’t really see inside the data from Wireshark, but my fear is the camera is saying “I’m 192.168.x.x” and the Mac is saying “I’m 100.x.x.x” because from the camera’s point of view, it would be receiving from “192.168.x.y” (the subnet router).
Since the feature is called HomeKit Secure Video I get the feeling they might be securing it by doing something like that.