PTSD diagnosis requires you to meet a set of criteria. A central one is direct or vicarious experience of threatened or actual death, threatened or actual serious injury, or threatened or actual sexual violence. In short, a significant, serious and traumatic stressor. Perhaps as many as 90% of us will experience at least one of these things in our lives, but fewer than 10% of us will go on to develop PTSD. Experiencing trauma is a necessary but, on its own, insufficient criterion for PTSD.

But back to trigger warnings. People with PTSD can be, and are, triggered by things that happen around them. Unfortunately, you can’t assume triggers that are overtly reminiscent of a traumatic experience will be those cues. Warning that a movie includes violence cannot be assumed to trigger violence-related stress, whereas otherwise innocuous things might. You can’t necessarily predict triggers.

https://www.noted.co.nz/health/psychology/trigger-warnings-psychological-problem/