Batman is Unmasked in Batman Vs. Superman Sneak Peak, but It Was All a Dream

Costume designer Michael Wilkinson revealed the context of this scene in an interview with Brazilian news site, omelete. 

As translated by WeGotThisCovered:

“It’s like a dream that Ben has, so we wanted to, it has almost a Mad Max quality to it where it’s like the end of the world, trying to survive and then of course Superman and his minions come, so it’s sort of a way of representing the amazing amounts of, the sort of obsessive quality that Bruce Wayne has about the threat of Superman.”