The alternative to me will be a rural farmer caught the disease through extensive farming. Contamination from a wild animal, directly or through livestock.

It then kicked around for months in a rural location, a lower R perhaps, with better weather conditions and less networked people. People died and family's moved on.

Until someone on a trip to the city passed it on.

Perhaps selling at the markets or perhaps to family there who then took it to the market through work or just shopping.

I would not write off the Lab theory, it's better than bats at a market, but there are other logical theories as well.