Or rather, a hypothesis disguised as an explanation. It ultimately said these nitrates come from farms, and this new datacenter is exacerbating it. The root cause is still the farms, though.
An explanation is just a theory that accounts for the facts. A hypothesis is a theory that accounts for the facts while also providing falsifiability and testability
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They didn't provide any accounting from facts. Did farms usage of nitrates increase? We don't know. Are there more or less farms? All we know is that they assert the datacenter now exists and since then nitrates have increased. It doesn't account for all the variables nor provide a likely explanation for how this could be true; it is only a possibility of many.