Sadly, Chester grew up being horribly abused and then using a lot of drugs. He was super close with Chris Cornell, who had also killed himself some months prior to Chester. Chester had been sober for a time but ended up staying the night alone after traveling and drank a little and hung himself on Chris's birthday.
Mike Shinoda has stated in interviews that when he and Chester would write lyrics, they would focus on the emotion and not necessarily just the exact experience. So the lyrics would slowly evolve until they both could sing them truthfully while relating them to their own separate lived experiences, which is part of why they can be so universally related to - because none of their songs are truly only about one specific thing, but rather about the feelings people experience.
Nope. That song came out when I was ten, so I had no clue it was about anything like that until probably a decade later.