Your assuming intentional release.
There could be all kinds of things they are working on ..as you said...the story about the membrane on the virus.
And safety protocol was breached.
It is not that far fetched to even think X bioweapons researcher guy accidentally spread it in the market.
Whatever happened, China is acting like it is a bioweapon. Maybe they think someone released it on them. Like North Korea, US, etc.
IF it’s an accidental release I’m sticking to my original hypothesis:
Improper building codes for the bioweapons lab. Corruption is rampant. Someone didn’t follow the building diagram to hook this to that (example, waste water was dumped directly into the river/lake/sewer instead of the biohazard handling facility).
Lab subsequently infested with mice/rats/etc. Creatures in the sewer exposed, etc.
Improperly handled research samples thus transferred to the outside animal population.
One of which was killed and butchered ‘messily’ and there we go...