root limbo

Hello,
This was my first time rooting and I'm a little bit confused. I followed directions as best I could but I've ended up in some kind of unrooted limbo.

I unlocked the bootloader ok. Put TWRP on my Nexus 5. Downloaded and flashed Euclideans nougat 7.1 which works fine!

But it seems that I have not superuser on my phone and when I try to install it through recovery, nothing happens. Both busybox and titanium backup say my phone is not rooted propery.

Has flashing this ROM unrooted my phone? I'm getting a little confused. Can someone help me?

Thanks