No, there didn't necessarily have to be a map change. One time I was on deathstar and we voted to extend the map, then everyone got disconnected. I got sent to the main menu with a notification like the one you get when you get kicked, but there was no reason given. When I opened and refreshed the server list, the server was empty. I had no problems with reconnecting thou. If I remember correctly the 2 servers on which this happened were EU Open and CA clan's Open server.
Also, it didn't happen again after these 3 instances which is strange considering how much I was playing today.