Presumably their coworker hadn't played the game.
I hadn't played the game or watched anyone playing it, and the only thing I knew about the plot before I watched the show was it was about a zombie outbreak and the main characters were a man and a teenage girl.
During the pilot I assumed Sarah and Joel were the main characters - they're presented as the main characters and it's exactly what I was expecting - so I assumed they both had "plot armor" for at least a season.
...
I also intentionally avoided any kinds of spoilers when I heard it was gonna be a show on HBO. I knew Pedro Pascal was the (co)star, but that's all I knew about the cast.