Apparently it was made at a local training center.
That's something different. If they took safety green fabric and made the shirt, then sure it can be done that way. I have yet to see safety green on a muscle shirt, typically it's silver, or some other off white color. Occasionally a black one, but more often than not a light colored one, occasionally a mesh fabric as well.
I don't know if I would sport a safety green one myself, but that's another matter. If it was custom made shirt though, I could see that happening a lot more than finding a supplier of them in bulk. I just don't think there would be that much demand for it.
Most of the safety colors I deal with either for sublimation or die cut vinyl transfer are still regular t-shirts, not muscle.