Can you be traumatized by something that didn't happen to you?

I have had a lot of traumatic shit happen to me and I've endured a lot but there's one specific thing that happened when I was around 8. It didn't happen to me or to anyone I knew. TRIGGER WARNING HOMICIDE: I watched a guy get hung upside down and slowly suffocate (it sounded like he was suffocating but I don't know how it works and it's all very fuzzy at this point). I didn't know the guy and his death didn't affect my life but I had nightmares about it for months and it haunted my waking hours too. Plus randomly in nights like tonight it comes back to me and I have to actively rework to build my walls and block it out but am I really traumatized by this? Or am I overreacting? I feel like it's pussy shit compared to really traumatizing stuff you know? Lots of people watch other people die. So what? I've seen objectively worse things since then and it doesn't bother me.But it was over a decade ago and it still pops up sometimes. I don't know is this valid trauma?