This is a Season reboot, not an entirely alternate universe.
In-Universe the population or the producers were so indignant at the end of V3 that they decided to rewrite everything on it. This includes Tsumugi's and Rantaro's memories. Unfortunately for them, memories are starting to fail, at least with Shuichi, Maki and Himiko, who are beginning to recover memories of their real talents.
This story takes place in a simulation whether or not it's the original cast
If it really is a Reboot the only possible ways would be that they are in a simulation, or everyone except Himiko, Shuichi and Maki are different people than Canon.
