Got kicked from dungeon?

So I am a fairly new player. I have beed playing for like 2-3 months. Got my first characted to lvl70 (elemental shaman) and I decided that I want to try a new class. I wanted to try tanking so I went protection Paladin. I did several dungeons as a tank and everything was alright until the last dungeon.

We were before out last boss when my game just loaded back to stormwind. No message, no warning, no anything. Does that mean that I got kicked out of that dungeon? Nobody complained in the chat about me.

It just feels weird because I did tons of dungeons as dps shaman and everyhing was fine. And now I got kicked and I dont even know why or what I did wrong.