It could just be a force vision. Imagine if this shot had been in the ESB trailer.
Let’s also not forget that the trailers for The Force Awakens showed us the shots of Kylo Ren and the Knights of Ren in the rain, which was seen in Rey’s Force vision. Not saying it’s true, but I do believe that seeing Rey on the Dark Side is very possibly a vision that Ben sees of her as Palpatine’s apprentice.