I feel it's more complicated than that. I wouldn't be surprise if Beijing does not actually know whether this was a lab leak or not.

The local government might know. They would have started a cover up reflexively.

But in either case, it could be that neither the local government nor central government wants to know or to find out. Ultimately, destroying the evidence and failing to cooperate with foreign investigators has cost China very little or nothing, even.

In short, I feel China should be admonished for covering things up, but not that the cover up proves the lab leak.