quantum mechanics - Why does a particle (charged) change sign passing the event horizon?

I have read this:

https://arxiv.org/pdf/hep-th/9907001.pdf

Where it says:

According to this picture, the radiation arises by a process similar to electron-positron pair creation in a constant electric field. The idea is that the energy of a particle changes sign as it crosses the horizon, so that a pair created just inside or just outside the horizon can materialize with zero total energy, after 1 one member of the pair has tunneled to the opposite side.

What I do not understand is, why does the electron or the positron change sign as it crosses the horizon? Is the horizon not a barrier where we have no info from anything that passed it? How can we know it changed sign? And why does the event horizon act like a charge changer?

I have read this question:

Does the electron really turn into a positron on $2\pi$ rotation?

And it says it is not possible as per QM to turn the electron into a positron, or vica versa.

Question:

1. 
   

   Is there any theoretical model for how the EH changes the electron into a positron or vica versa (is it theoretically possible at all to change sign)? Is the event horizon like a charge changer?

   
   


2. 
   

   If no info can leave the inside of the EH, how do we know about the sign change?