Why is my iMac booting without HD and CD drive!

Hi All. I hope I am having a stupid day or not seeing something obvious. I have a 27" iMac mid-2011. I installed a brand new HD, which still booted to the old account details. So, I thought maybe the SuperDrive was turned into a secondary HD, so I disconnected that, but I still get the same!

I have done the usual stuff SMC/PRAM reset. I also completely dismantled this iMac, and I couldn't see another HD or anything that would make me think suspiciously.

I am hoping there is a simple explanation. Can someone advise/help?

Thank you.