That requirement/disclaimer was present on the Steam store page the entire time the game was actually available for purchase.
The main issue was that it was not actively enforced due to server issues at the time - which the studio CEO acknowledged:
> I do have a part to play. I am not blameless in all of this - it was my decision to disable account linking at launch so that players could play the game. I did not ensure players were aware of the requirement and we didn't talk about it enough. We knew for about 6 months before launch that it would be mandatory for online PS titles.