Class 1-A had been hit with a quirk collectively which they had brought up with the staff members of UA which they had then deduced was a time travel quirk meaning they would go to some timepine that wasn't their own. The staff had told class 1-A how to keep themselves safe and also prepared for whatever could he thrown at them when that timeline came to the 2100's where they were.

Class 1-A and the staff stood in the courtyard in a row and they felt the wuirk taking affect. Each of them could feel the quirk taking affect and before they knew it they were teleported into the past and a new set of students were teleported in their place. You and your class. Judging from your clothes they could safely say that you all were from the past. The staff were on guard just in case they had to act.