[decorator]

You're assuming with certainty that there was a causal relationship. Given that assumption you were comfortable in proclaiming the counterfactual to be true. You "knew" it was true because you "knew" the mechanics of the world, thus could predict the counterfactual truth-value.

Did you use something like Hill's criteria for causation[0]? To establish anything? Like in epidemiology? It's how they can make such statements.

I do take your point about how one can be somewhat certain of a counterfactual. You couldn't be though; because you've got no criteria by which to judge the causality.

[0] https://en.m.wikipedia.org/wiki/Bradford_Hill_criteria