Honestly, I can't find the result referenced in the article, nor in a similar article posted to SCMP. It might be because I'm searching in English, didn't dig too deep. My guess is that they added a gene that codes for Dsup[^1]. I don't think Dsup is well characterized mechanistically. I think it probably mostly protects DNA from secondary damage from ionizing radiation[^2], so protection from radicals produced by ionizing radiation, rather than direct breaks to the DNA itself (though maybe, I'm not familiar with research in the field).

[^1]: http://dx.doi.org/10.1038/ncomms12808 similar research noted in another comment as well. Note that most likely the novelty of the OP research is using CRISPR instead of the transfection method cited in the paper.

[^2]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6773438/

The article is great in giving no scientific context and not even linking to a reference.

I assume they talk about Dsup (https://en.m.wikipedia.org/wiki/Dsup), an enzyme preventing DNA breaks by stabilization. DNA breaks are caused by radiation and are what causes mutations (increased cancer risk) and in the extreme case cell death.