It's common to see misattribution like this happen woth media, and it's really not a big deal that someone is caught unaware. Like Thief actually does get a lot of praise and did impact gaming, but it's easy for someone to not know of it depending on who they talk to.

But the worst example is several users and a couple YouTube essayist claiming Assassin's Creed 2 was revolutionary, when it was basically doing nothing new, and was just ironing out the formula that was 99.99% established by a game that seemingly none of them heard of called... Assassin's Creed 1.