[toasterlovin]

There was an intervention (telling people not to eat fat) based on the "eating fats = bad" hypothesis and that intervention failed to have the effect that the hypothesis would predict. That is disconfirming evidence. You are correct that it's not conclusive, but it is disconfirming nonetheless.

That's all I am saying.

[sykhotic]

It’s not disconfirming since it’s possible that eating fats is bad but also that replacing fats with sugar is bad too or possibly even worse than eating fats. There are also other possibilities to explain why eating too many fats is bad even though when they were targeted for reduction health outcomes did not improve.

[toasterlovin]

It disconfirms the original hypothesis. You have mentioned other, more complicated hypotheses which it does not disconfirm.