The other source is a nature news article [1] which has by now following disclaimer:
> Editors’ note, March 2020: We are aware that this story is being used as the basis for unverified theories that the novel coronavirus causing COVID-19 was engineered. There is no evidence that this is true; scientists believe that an animal is the most likely source of the coronavirus.
It also states at the end:
> Without the experiments, says Baric, the SHC014 virus would still be seen as not a threat. Previously, scientists had believed, on the basis of molecular modelling and other studies, that it should not be able to infect human cells. The latest work shows that the virus has already overcome critical barriers, such as being able to latch onto human receptors and efficiently infect human airway cells, he says. “I don't think you can ignore that.” He plans to do further studies with the virus in non-human primates, which may yield data more relevant to humans.
So it might just as well be that these experiments warned us about that potential, and now that it actually happened, some people interpret the original warning as the cause.
[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4797993/
[1] https://www.nature.com/news/engineered-bat-virus-stirs-debat...
Unfortunately, SARS-CoV-2 is a very contagious virus, so it's hard to contain. A lot of ink has been spilled about the Wuhan BSL-4 lab, but these viruses were only considered to be a BSL-3 pathogen, and were handled in Baric's lab at UNC in their BSL-3. I would assume that they would also have been handled at the WIV's BSL-3. There had been reports of biocontainment lapses at the WIV, and there have been a number of lab escapes of various pathogens including SARS at other Chinese labs.