Made to act 3 and wanted to play in a party and joined up with someone.

Apparently he had played through act 3 already as I joined him at the end of the map. Since I wanted to at least made it myself there without skipping the story I left and started a solo game, but now I also need to start there as I that's where the quest marker is at while before that I had to do one of the Wings still.

That normal?