Connection between Mai and Arata

Oh, that's the first solid connection to the first game of the series aside from Shina being present. Apparently, back when she was at her father home, Mai hacked in the Enigma Games servers and got discovered by Arata that left her with a file that she kept up to this day. That file was the key needed to unlock the laptop that they found in that house.
I'm still totally confused if this is a virtual world or reality after they mixed as we saw in the epilogue of the first game though.
The monsters feel like something that would come out of a game, but with the pollution of the real world...we really couldn't tell can we?