I'm still betting that one of two things happened.
1: Stevonnie jumped into Padparadscha's head and saw a vision of the past, mixed with a dream, relating to the planet that way, since it's clear that Lars and crew were already in the planet's atmosphere at the time.
2: Stevonnie jumped into Yellow Diamond's head while dreaming, and the dream mixed with Yellow Diamond's memory, resulting in the vision we saw.
Before anyone says anything about either of these, keep in mind we don't know how far the dream entering thing can go, making Yellow a viable memory candidate, and Paddy's visions have all been related to the environment around her, so it's not that far-fetched to assume that she could pick up on a long-past event if it was the first time she's ever been close enough to a location, which is a safe assumption to make for now, since we don't know how she wasn't shattered upon emerging. Or the dreamstate thing could just amplify her powers, we can't really know for sure about anything yet.
I think we need to see more of what Pink can actually do before we go making wild theories, we still know very little about The Diamonds and their powers in general.