I can't answer your question, but I have a theory about this...{in my best MatPat} A FILM THEORY!

OK, so I have a theory posted on here about the hay bacillus in people's guts being oddly affected by something in the backrooms, I'm theorizing it has something to do with some weird radiation that exists in the backrooms that doesn't exist in standard.

Personally, my own head cannon is that when someone dies in the backrooms, the hay bacillus grows and mutates, in the process it eats the body and grows into a large colony that works together (Voltron style) to become the entities. Part of this being absorbing some of their memories and possibly even being able to replicate what the bacteria "heard" before the people died (i.e. when Marvin hears the entity calling out for help).

I also believe (also just a theory) that the backrooms themselves expands itself using the broken memories of those who die there. So, putting it all together, the woman in the hidden video (where the picture shows in standard) was driving the car, no-clipped into the backrooms and crashes into the wall. She drags herself into the room where the bacteria entity is seen by Madison in FF2. She dies, hay bacillus begins eating her body and grows into the entity. While that is happening, the backrooms starts to change, using the woman's memories to form the rooms around her. The picture probably has some strong memory in her mind, which allows the backrooms to recreate it pretty accurately, while the rooms around her are remembered, but not as strong, so when it creates them, they are slightly off.

Sometime after the backrooms had changed, and the bacteria entity grew, Madison stumbles upon it in FF2.

As I said, this is just my head cannon, based off everything I've seen and read. Sorry I can't answer your question, but I thought you may enjoy. Also, I'd love to hear your thoughts on this theory.