There is a known dramatic climate shift that occurred around that timeframe that is responsible for several civilisation collapses. [0]
However, the author points out that they lack the preservation of proxies such as what you've pointed out. They were analysing in a region where ecological change occurs frequently.
Well, with that being said, what I read, at least to some extent, implied this society had a (heavy) hand in their own undoing. But if the area is known to be in flux, then maybe it was simply another round in that cycle? Or not?
That context, to me, should be stated plain and obvious right upfront. Caveats. They matter.
However, the author points out that they lack the preservation of proxies such as what you've pointed out. They were analysing in a region where ecological change occurs frequently.
[0] https://link.springer.com/article/10.1134%2FS106422931707001...