Properly update a rooted Nexus 5X with stock Android 7.0 to October Security update When I bought my Nexus 5X, it had Android Marshmallow on it. I immediately rooted it and flashed TWRP using the Nexus Root Toolkit (NRT) and it went well.

Along came the Android 7.0 OTA and I only had to remove the saved fingerprints and PIN (to make TWRP see the phone as decrypted) I was able to go through the update successfully with that current setup. Of course I had to re-root my phone after that.

But the 46.7MB October Security Update won't install via OTA. I've tried:


re-rooting it with the latest TWRP (via NRT)
re-flashing the stock recovery (via NRT)


but the OTA still wouldn't get installed. I checked the recovery log and it showed this line:

installing lge.bullhead updater extensions
Source: google/bullhead/bullhead:7.0/NRD90R/3141966:user/release-keys
Target: google/bullhead/bullhead:7.0/NBD90W/3239497:user/release-keys
Verifying current system...
script aborted: E3001: Package expects build fingerprint of google/bullhead/bullhead:7.0/NRD90R/3141966:user/release-keys or google/bullhead/bullhead:7.0/NBD90W/3239497:user/release-keys; this device has google/bullhead/bullhead:6.0.1/MMB29Q/2480792:user/release-keys.
Source: google/bullhead/bullhead:7.0/NRD90R/3141966:user/release-keys
Target: google/bullhead/bullhead:7.0/NBD90W/3239497:user/release-keys
Verifying current system...
E3001: Package expects build fingerprint of google/bullhead/bullhead:7.0/NRD90R/3141966:user/release-keys or google/bullhead/bullhead:7.0/NBD90W/3239497:user/release-keys; this device has google/bullhead/bullhead:6.0.1/MMB29Q/2480792:user/release-keys.
E:unknown command [log]
Updater process ended with ERROR: 7
I:Legacy property environment disabled.
Error installing zip file '@/cache/recovery/block.map'
Done processing script file


But I checked the build.prop file and found this:

ro.build.desciption
google/bullhead/bullhead:7.0/NRD90R/3141966:user/release-keys


Where could that google/bullhead/bullhead:6.0.1/MMB29Q/2480792:user/release-keys have come from? How do I proceed with the OTA? I've yet to try FlashFire because it won't detect the downloaded OTA file and I've yet to download that 1.2GB factory OTA file.

Also why only now am I having problems with OTA? It should have happened during the Android 7.0 update, right? I would like it very much if I could do this without wiping my data. Please help. Thank you.
From XDA Developer's [GUIDE] Unlock/Root/Flash for Nexus 5X, I went away and:


Downloaded the OTA zip file
Installed the Android SDK tools,
connected my device and rebooted it into TWRP
Then went to Advanced -> ADB Sideload
Then from the command prompt, typed "adb sideload /path/to/OTA/zip/file" and hit enter
It took a few minutes to 100%, then I rebooted my phone and all is well and updated now.
Re-rooted my phone using NRT.