I think the fact that Kylo is wearing the mask in Rey’s vision is because the scene was probably originally shot with the mask on. If you look at the first trailer with Kylo in the woods, he has the hood on which means the mask also.

They probably reshot the scene with Kylo without the mask to make it more dramatic or to change something. The shot of Kylo in the forest with his mask is just a leftover from the unused sequence. Also it could be they hadn’t revealed Kylo’s face yet in the movie and so just used the mask in the forest to hide his face until the reveal.