I haven't seen any refutations of these claims apart from "those involved say no". There's a nonzero chance that these people are lying to cover things up or protect their reputations. Millions of deaths being attributed to a lab accident would be pretty damning.
Why do people on HN want this to not be the case? (As evidenced by all the downvotes?) The truth could be anything, and we should be looking for it. This is one possibility that carries a lot of weight and demands our attention.
There's nothing wrong in stating that the evidence is substantial and that we should investigate more. Why put your head in the sand?
This isn't anti-science.