Carrier lock and Bootloader lock are different things
The devices solded standalone, were not linked to a carrier network.
Some devices were initially solded by the carrier at “special low price” associated with a 2 years mobile plan contract and devices were locked on this carrier network
they can be unlocked by the owner after 6 month if they ask for the unlock code.
If it was not already done, one can unlock the device access to network if a customer of the concerned carrier ask for the unlock code for the device (you need to specify the IMEI)
NO
Carrier Unlocking has to be done from the stock carrier firmware. BEFORE installing a custom OS.
Some time ago, it was well noticed as pre-requite in the install doc but now the caution have disapeared