There’s nothing particularly new about lab escapes, they happen quite frequently. And given the presence of a bio-lab studying coronaviruses just a short distance from the site of the first reported cases, why would any rational person not consider that as a possibility?
I don’t think you even have to go down the “bio weapon” route here. It could be as simple as a worker infecting themselves with a natural sample unwittingly. Following your logic then, I think China would be incredibly unlikely to admit a lab escape of a natural sample now given the devastation it has caused. It’d be a huge loss of face and draw questions towards China’s competence.