Lack of transparency in China proves nothing. CYA is standard operating procedure there, regardless if there is any guilt or not. Up and down the chain they will cover for each other, if not for the simple reason they themselves don't know what shit their superiors or underlings are up to...

And it is entirely rational, even when they believe that there hasn't been a lab leak, to shut down any investigations into it, because all such work or information would just add fuel to the fire, regardless the "objective" outcome.