I don't know what you're getting at. I can only get two different things out of this:
1. You're specifying that it wasn't listening to headphones at low volume because it was loud SX that caused it. I am saying that such a distinction is irrelevant because sharp increases in volume are inevitable.
If you hear a loud sound in your headphones, then it doesn't fit the definition of using them at low volume, does it?
I hope the following doesn't sound patronizing: it's not intended to be, and it is not as obvious as it seems (the last paragraph before the next quote will show why): perhaps you are not familiar with how the volume setting of your headphones works, but it is generally a slider that is either physical (embedded in the hardware) or logical (as software), which will essentially limit the amplitude of the voltage that ends up feeding the actual drivers (ie the speakers that sit near your ears).
So if you were to listen at low volume, that max voltage would have been set such that even the loudest signal being fed to your headphones would be clamped down by the voltage limiter, and not cause an acoustic trauma.
The danger happens when you listen to soft sounds (which are represented by low amplitude voltages) on headphones that do NOT have the volume slider down (ie they are not being set to "low volume"). You do perceive those sounds at fairly low volume, but the volume slider does not protect you from surges. If you have a high voltage "surprise" in your content, then you will actually feel it as loud through your headphones. I suspect that is what caused your acoustic traumas.
I think you are confusing "I'm hearing something softly through my headphones" and "my headphones are set to a low volume": you can be listening to soft music on headphones that are set to max volume. That is dangerous!
A common trap is to use apps on computers that have their own volume slider: let's say you have your music app with its slider set at 10%, which you rightfully feel is soft. What this doesn't show you is that the computer itself may still have its own volume set to the max! So you're happily listening to your music, and all of a sudden some other program makes some sound (for example, an incoming email notification sound), which isn't being clamped by your 10% setting on the music app! Instead it'll come out full blast!
This is a trap that is easy to fall into: I admit I've gotten a few close calls myself.
2. You are doubting that headphones actually caused my T/H.
I don't doubt that the headphones were the tool by which your T/H came about, but I think the loud noise that you fed your ears through your headphones are the problem, not the headphones themselves.