Step one, are we still debating whether or not this was a bio-weapon?
Actually, I'd like to see evidence of man-made gene-editing or reverse-engineering.... so far, I've seen none.
Only speculation "it could" or "it's not ruled out completely" <-- which is true, because science doesn't work in absolute terms, and actually welcomes criticism. But not speculative one, it should be based on facts and findings.
In the end, scientists will always look at the presented data and then pick the most likely, and most easy solution, to formulate an accepted allaround standpoint. It's not arbitrary at all, but also never 100% sure either.
One thing to keep in mind is that viruses kill indiscriminately and without borders. So even if a nation constructs one as bioweapon - they would look for a vaccine for their own people in the first place before releasing this... so only a madman or some sophisticated terrorists may come into play - but why would they only release it in one place only when they could've send that to numerous places simultaneously with ease?
Esp. the fact it started in a single location is a strong indicator that it happened/evolved accidently.