That’s 2x 3:15 (approx), plus turnover, preparation etc we are getting close to 8h. Are we to understand that they were operating another rotation before (presumably a short one) ? Those are pretty heavy work days :/
Don't know what the company scheme is but EASA can allow (I think) as much as a12:30 FDP even before any discretion comes into play....
As for what went before the BHX-CFU for the original crew, who knows? Some forms of standby start the FDP clock ticking, positioning by air/road to BHX? Ultimately all sorts of things are possible....