The Extra Helper.

The reason they felt a sense of strangeness and déjà vu when they entered this place was because they had actually been here before. This place felt like the space of the realm heart of the High Heaven realm that they experienced before because it was the space of the realm heart of the High Heaven realm. 

They were stunned and shaken.

Legion-8 asked in disbelief, "How could this be? Did we travel back to the past?" 

Legion-7 scoffed, "That is not possible. There was no era of conquest in the past. It is more likely that the dragon's clone fight with Mother High Heaven has not ended. Maybe everything we experienced since the dragon clone made contact with her was fake."

That explanation despite how ridiculous it sounded was the most reasonable explanation they could come up with for why the space of the realm heart of the realm of high heaven is identical to the space of the realm heart of the Tyrant realm.