He was being a dick. He was like “but I listed it as locked! You should’ve read the description!!!” And I was like “no dude, you said it was CARRIER LOCKED. You didn’t say it was bloody account locked!”.

That phone was 100% stolen. I bought an android tablet many years back with a similar story (account wasn’t completely removed), the seller was all “get it back to me I’ll happily unlock for ya”. Your seller was “it’s locked” because he couldn’t unlock it.