No reason to be concerned. We had a server problem with the Main Arena this morning. We took it offline to see if we could figure out why and put up the "Main Arena 2" so people could play.
When we put the original Main Arena server back online, we renamed the other arena "Backup Main Arena" and re-opened it in case the "Main Arena" starts to behave badly overnight.
It is just a backup plan to insure everyone has a place to play.