That section is dealing purely with an attacker who wants to impersonate a ChannelID. It's correct that an attacker cannot fool the real server into believing t

That section is dealing purely with an attacker who wants to impersonate a ChannelID. It's correct that an attacker cannot fool the real server into believing that it is in possession of a ChannelID, even if the attacker has the server's private key (so long as the server is forward secure). However, that doesn't mean that the client isn't fooled. (Disclosure: I wrote that section of the draft.)