How is this possible? This player in Steam already completed the hidden achievements from the upcoming DLC?
Hack his/her steam account and see what they are. 11
On serious note, could be a bug.
Probably he/she used a third party software like Steam Achievement Manager. No big deal.
Could be a FE dev who unlocked them for testing purposes maybe?
He unlocked also the other old all at the same date and time, most sure he used the achievement manager, sad that the passed hidden achievement didn’t reveal information after unlocked.
They used Steam Achievement Manager to unlock the achievements manually.