It doesn’t even have to be an escaped laboratory experiment. Reportedly, the Wuhan laboratory was studying coronavirus vaccines using bats. There were also reports that there were security incidents where researchers and / or technicians were bitten by the bats.
It is not unreasonable to believe that the laboratory staff made purchases in the affected wet market.
Laboratory workers get COVID from bat bites and then spread it to other people while shopping in the wet market.
This fits well with known facts and the assumption that humans eat infected bats.