There's a big difference between "with perfect certainty" and "with any degree of certainty". We can't be pefectly sure that the scenario you outline didn't ha

There's a big difference between "with perfect certainty" and "with any degree of certainty". We can't be pefectly sure that the scenario you outline didn't happen but the timing and the idea of a virus acting like that are so improbable that we can be almost entirely certain it didn't play out like that. We're not perfectly certain it was the impact, but we are very certain with all the evidence that has built up.