I think he means enable usb debugging.
normally you have to enable dev options > usb debugging then approve the device when first connecting via adb.
on a brand new phone, you can boot to bootloader without ever loading the OS, go to fastboot devices (the device won't be authorized), however as long as it shows the device is recognized, you can type fastboot oem unlock, then do it again and it will unlock without having to have previously booted to OS, unlocked dev settings, enabled usb debugging, authorized the device/computer via adb.
before I learned this, I used to boot up the phone and *skip* the google login, enable dev, enable usb, authorize ADB, then reboot-bootloader, then finally fastboot oem unlock