Thank you for your thoughtful comments.

I must say that that's one flaw of the hypothesis. The MMP hypothesis speculates that the decades of evolution were condensed in the miners, which remains unproven.

One possibility I can think of is that the miners were exposed to the RaTG13 virus for a very long time already. Their weakened lung immunity further allows the RaTG13 virus to stay and evolve inside the host. It is only when they got sick enough to get hospitalized that SARS-CoV-2 has evolved. But again, it's just a thought.