Can the frozen-food theory be a credible explanation of the conduit conundrum? No. But it's good the WHO brought it up, because it takes the investigation in an important direction: the need to find conduits that could have delivered the virus to Wuhan. These conduits would need to meet the WHO's criteria: they'd have to be animals that make good hosts for the virus, they'd need to have had opportunities to interact with the bats known to carry these particular coronaviruses, and they'd need to have traveled directly to Wuhan from the rural areas of the region without ping-ponging all over South China.
That sounds like a tall order. What are the chances of finding documented proof of such vectors? Remarkably, however, we actually have a wealth of evidence that fits this description perfectly: human beings—the best SARS-CoV-2 hosts of all—who had extremely close contact with horseshoe bats in South China. We know they made repeated visits over many years to the exact caves where SARS-related viruses were found. There, they handled bats directly, spent extensive time inside the caves breathing the air, and brought thousands of samples of guano, blood, and other bits of bat (possibly even live bats) back to Wuhan with them.
Those were researchers from the Wuhan Institute of Virology, who had been scouring South China caves for coronaviruses with the ability to infect humans. They did this as part of a massive virus-hunting project—a collaboration between Peter Daszak's EcoHealth Alliance, the USAID's Predict program, a new organization called the Global Virome Project, and other groups—to track down the world's viruses in their lairs, bring them back to the lab, and study them. They would pay special attention to the ones with the ability to infect humans, learning how they enter cells, how they mutate, how they jump from host to host, and how they escape the immune system and persist in individuals.