Many of the extras are in both fancy costume or Halloween costumes.
Included on this picture is the intense blue outfit and pink cape of Superman.
The iconic S is even emblazoned on the again of the cape, proving certainly who this costume is of.
It seems to be like the person sporting the costume is not Henry Cavill, the present Superman.
Despite this, it definitely does show the existence of Superman within the new Matt Reeves-penned Batman franchise.