Similar to if we had a sudden large radiation hazard and it was unclear if it was some spontaneously emerging phenomenon with essentially no direct human cause, or a power plant/enrichment facility/warhead manufacturer/etc.
And beyond that, there are supposedly methods of (even purely scientifically motivated) research that would involve engineering a virus with certain properties that also happen to make it extraordinarily deadly.
Ethics committees determine all sorts of experiments to be prohibitively unethical, and a virus with particularly deadly design should certainly be held under such scrutiny.
"Yes, come right in, here's our primary source data collected, it concludes that Chernobyl (or WIV lab leak) did happen..."
Suddenly China's rapid detection and extreme lockdown would literally be properly contextualized as buying the world time, and the Chinese system would be validated beyond measure.