It sure looks like it, although I can’t confirm that, as I waited for the new Fairphone Android update and associated SPL. However, I did see that letting it boot into Android post-flash caused get_unlock_ability to return 0, so it seems likely.
Allow me to answer these questions with some (pseudo)code, which I think better highlights the order and results of my actions. 
Flash the Fairphone (Gen. 6) with the Fairphone Android OS.
# Desktop PC is running Linux.
# Phone is running /e/OS 3.0.2, SPL May 2025.
# Phone has a fully-unlocked bootloader.
> adb devices
# Confirm USB debugging is working by detecting phone.
> adb reboot bootloader
> sudo fastboot devices
# Confirm phone is visible to Fastboot.
> sudo fastboot flashing get_unlock_ability
# Returned 1.
> sudo ./flash_fp6.sh
# Scripts starts flashing the phone.
# Once completed, hold VOLUME DOWN to boot into Fastboot instead of Android.
Locking the bootloader, part one (lock_critical).
> sudo fastboot devices
# Confirm phone is visible to Fastboot.
> sudo fastboot flashing get_unlock_ability
# Returned 1.
> sudo fastboot flashing lock_critical
# Phone prompt: Are you sure you want to lock the bootloader?
# Yes.
# Phone clears and resets.
# Hold down VOLUME DOWN to boot into Fastboot instead of Android.
Locking the bootloader, part two (lock).
> sudo fastboot devices
# Confirm phone is visible to Fastboot.
> sudo ./fastboot flashing get_unlock_ability
# Returned 1.
> sudo fastboot flashing lock
# Phone prompt: Are you sure you want to lock the bootloader?
# Yes.
# Phone clears and resets.
# Allow phone to reboot into Android.
Hope this helps, and if not, do let me know so I can clarify further! 