That is indeed a picture from the past and not the little Uraras we know. If I remember right, in Volume 6 it hasn't even been a year after Volume 3. It definitely feels more serious overall, but that might also be the art style that's changed.
Correction of a silly mistake in this chapter: On page 12 Spica says that the foreign creatures aren't originally from there. Nothing about Nix's origins. This seemed like an important enough difference to address so that nobody is confused by future revelations about Nix.