Sorry, it's not really meant to be a secure chat.
It's catered to people who don't want to signup or install anything. Who just want to go to a link and start chatting.
Still, it'd be worth putting up a notice somewhere that users can't expect privacy from this site.
As for the room IDs --- randomizing them is a fine bit of rubber-chicken security. I think it's a good idea. But the right solution is to allow users to erase the chat logs, and to verify that users have access to a given room before dumping all messages starting at message ID 0.