> the causal pathway

The article very clearly distinguishes between the cause and a cause. "Alzheimer’s is a complex disorder, not a one stop shop" and so on.

> best explained by correlation than causation

They did more than that. They also found gingipains in the brains of patients. Those had to come specifically from P.gingivalis infection, not the other factors you mention. They identified a plausible causal pathway involving tau and amyloid beta, and they induced their production by introducing P.gingivalis in mice. That's a lot more than merely equating correlation with causation.

Skepticism is good. Ignoring what has been presented is not skepticism, and neither is jumping from correlation to non-causation. That's just contrarianism.