It's a possible explanation, but that doesn't mean it's "very likely". In that case it would be easy enough to drive back down to the cave and collect the missing evidence of bat origin. Better yet, you'd never have to disclose the low-level employee part, so there'd be no political fallout. Easy win.

Also, my understanding (quite possibly wrong) is that while humans can get sick from bats, as cave workers did in Southern China, those viruses aren't contagious in the sense that the sick humans go on to infect others. "Since no case of an epidemic caused by direct bat-to-human transmission has yet been demonstrated, it is thought that the transfer to humans more probably took place via an intermediate host species in which the virus could evolve and move towards forms likely to infect human cells." [1] If that's right then your explanation of spilled bat samples is incomplete: it doesn't explain what caused the bat samples to adapt into a form that could spread among humans. That sort of puts us back at square 1. Another way of saying this is that if your explanation is likely, then we'd have expected the pandemic to have started where the bats are - through sick cave workers or something similar. But in fact it started far away.

[1] https://news.cnrs.fr/articles/the-origin-of-sars-cov-2-is-be...