You must check if the approach is clear before you cross a runway. If you can't see it, you use TCAS. There is no excuse. Furthermore, I think they could have seen it because they do have visibility in that angle.
And runway crossing in Barcelona is done on the tower frequency. So they would have been on the same frequency.
The airbus seem to have their strobe lights on, so they would have been aware they were crossing a runway because on a taxi way you don't use strobe lights normally.