Flashing factory image didnt return to stock!

I had on my nexus 5 custom recovery, custom kernel (franco) and paranoid android rom (rooted). I wanted to get back to stock and flashed factory image lollipop 5.1 doint this
adb devices
adb reboot bootloader
fastboot flash bootloader <bootloader-filename>.img
fastboot flash radio <radio-fileame>.img
fastboot reboot-bootloader
fastboot flash recovery recovery.img
fastboot flash boot boot.img
fastboot flash system system.img
fastboot flash cache cache.img
fastboot flash userdata userdata.img
fastboot reboot
When i rebooted i noticed that everything was fine but i had paranoid android rather than stock rom! What happened?