Quick theory time:
If we go frame by frame in the beginning, we can see a massive purple tornado really did hit Midgar:
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I know there's a lot theories going around that the news broadcast is either Shinra propaganda or Sephiroth mind-fuckery, but I'm going to take it at face value. After all, a tornado was shown and it needs to have some consequence.
I think we can all agree that the tornado is somehow linked to the events that transpired at the end of Remake. Namely, the Whispers' defeat. So let's consider what we were shown afterwards.
Immediately after the Edge of Creation scene, we are shown a scene of Rufus meeting with the Shinra executives. Yet the news broadcast claims that Sector 0, where the Shinra Building is situated, was hit hard. Why is there no damage?
Later, in Remake and Intermission's ending, as well as in Rebirth's recent trailer, Midgar is shown in the background. Again, there is no damage to the Shinra Building.
Additionally, when Zack arrives at Aerith's church in Intermission's ending, the people are distraught and in disarray, while a haunting version of Aerith's theme plays.
Combining this all together, I'm proposing that the purple tornado
didn't hit the Midgar we played through in Remake. It hit the Midgar in Zack's scenes, injuring/killing Aerith, Barret, Tifa, and Red XIII (note that Cloud is absent).
We're presented with two different versions of Stamp, and now two different events at Midgar. That points to multiple universes.
The party exited the Singularity into their own universe, the one featured throughout Remake and Intermission. However, their actions affected another, the universe where Zack's survival takes place.