Default Backed up stock rooted ROM with TWRP And now asking for encryption password?

I backed up my D800 using TWRP and once the phone rebooted it is now asking me for an encryption password? Not sure how that happened but can someone point me in the right direction?

EDIT:Okay so i held in the power button, clicked power off and restart and now I'm booted back up to how it was. Still no idea why that happened?