To be honest I think it's absolutely bonkers. I simply don't see the sense of selling 2 identical discs in the same package. Seems totally pointless to me.
A member on another forum intended to buy the DVD but didn't bother at all in the end. No point paying £15 for two identical discs, whatever the format (why would Blu-ray owners need a DVD copy too?). I don't see why Arrow couldn't have increased their sales by selling two separate releases.