If when you see a plane flying low you hit the ground and start screaming, that's certainly a disorder. If you glance up at the plane and feel "hrm, I don't like it much", that's not really a disorder. In between those two extremes is found the difference between PTSD and "I don't like low-flying planes since 9/11".
Now that I think about it, I also get freaked out in moving crowds now, which I never did before. (I can be in crowded places, no problem--it's just when a lot of people are moving and mixing, like at a parade, music festival or busy shopping district.)
The airplane thing is totally manageable; I just need to stop and take a few deep breaths. The crowds thing starts off that way, but can get outright panic attack inducing if I don't get somewhere less crowded, and quickly.
I'm with OP. It seems that to be a 'disorder' it needs to have outwardly visible and functionally maladaptive outcomes on your behavior.
Are these really PTSD symptoms? I have the same thing, though perhaps not as bad. I was 5 miles from the attack, and in fourth grade at the time.