Queued in by myself in lobby & at the actual balloon pq Not sure if this is a bug or someone just left at the last minute or just unlucky. Also people are opening up monster bags in the entrance and killing people lol.
I'll throw my prediction You were probably an unlucky soul that didn't manage to join a 6 party team. Think that people enter this pq waiting zone, and the game starts as soon as the wait timer runs out. Nothing guarantees that when that timer ends, the amount of people in the map will devide perfectly to 6. There will almost always be leftovers. So my guess is you were a single leftover on that run. I bet people started stuff like 2v2 runs and 1v1 runs before as well. I had a 2v2 run after one of my party members dced right in the waiting room.
It's possible and intended. If there are not enough players to do a 3v3 for everyone, it will choose teams for a 2v2, 1v1, and finally a 1v0. There is actually enough time to kill the balloon if you are solo!