That's it? What a letdown.
Jeez, even if this exchange had happened on television, it still wouldn't have proved anything beyond being a meta-joke for the audience.
My take remains the same as always: Superman (and Supergirl too) do not exist on the same world as ARROW / THE FLASH / LEGENDS OF TOMORROW, but they will be able to do a special crossover via parallel Earths in a season or two or three down the line.