If it can be demonstrated that the virus came from a bat that is not from that area, and the only bats of that type in Wuhan are being used for testing in the lab, that would seem to be proof that the virus came from the lab.
How else would be virus get to Wuhan if there are no other bats of that time in Wuhan?
Or: How much virus could a Wuhan bat bat, if a
Wuhan bat could bat virus?