Does "unlocked" mean carrier-unlocked or bootloader-unlocked? I'm confused by this sentence:

For example, Artem's unlocked stock Pixel is still on Widevine Level 1, the most secure level, but fails SafetyNet because it is unlocked.

(What does "unlocked stock" mean - does the Pixel ship carrier-unlocked? Was it unlocked by calling up the carrier and asking for an unlock, or in some other way?)