Trauma is a sophisticated concept. As a society and species, we are pretty “trauma naive” in that we have just recently come to this understanding of the very complex web of psychological, somatic, emotional, sociological, intergenerational, and cultural aspects of this experience. Because of this, we are refining the therapeutic modalities that are most efficacious for treating trauma. See all the latest literature by Peter Levine, Bessel van der Kolk, Gabor Maté.
So I wouldn’t really expect these societies to know what to look for - in fact, it could have been so ubiquitous that the symptoms (and/or suppression of them e.g. regular intoxication) were normalized.
Given how warlike they were as he described in the article, it could be like asking a fish to describe water.
We know for a fact that mammals get PTSD after being in highly stressful experiences that they are unable to metabolize. I can’t see why humans would be any different.
Also, many different cultures have historically had taboos around the expression and natural resolution of PTSD. I don’t know about the culture of society around the age he is speaking of in this regard, but I wouldn’t be surprised if that was a normal aspect of life back then, too.