Wow, that is really weird. You should only see that message if two players used the same player nickname "Fjubiekl54juw3akrfm". That is not likely.
The room features are very new and basic. They will get better over time. I see some things to fix, but they are different problems.
Some older browsers can play the game and do WebRTC, but cannot connect without Trickle ICE. I need to fix this too.
I'll keep looking for the problem to fix it.