I don't know how to describe this

I was in lobby for a game when my screen went black and a message popped up saying "A match has been found" and a 30 second timer and 2 options came up that said "Continue what I was doing" and "Join now" so I clicked join and it brought me to my old lobby and then the screen was black so I closed out the client but didn't have a time penalty? What just happened?