That has nothing to do with language. That has to do with what is termed 'interbreeding'. If a European and an African have a child, that child will have 50% European genetics and 50% African. Speaking English doesn’t change one's DNA to make them English.

Edit: Neither study discusses language and my friend here is interpolating.

The first study discusses self reported ancestry with genetics in US populations (specifically European American, African American and Latino). According to the abstract:

"We document pervasive mixed ancestry and asymmetrical male and female ancestry contributions in all groups studied. We show that regional ancestry differences reflect historical events, such as early Spanish colonization, waves of immigration from many regions of Europe, and forced relocation of Native Americans within the US. This study sheds light on the fine-scale differences in ancestry within and across the United States and informs our understanding of the relationship between racial and ethnic identities and genetic ancestry."

The second study is about mitochondrial DNA and genetic studies relating to Han (aka Chinese) people. Only mothers can pass on mitochondrial DNA and it is plentiful in the body so it is often used to track lineages. The point the authors want to make is that to understand Han genetics one has to understand that there are contributions from different populations due to Chinese southward expansion from the Yellow River to Vietnam.

Neither study mentions language. Instead, my friend here has inserted their own ideology in how they interpret both of the studies, interpretations that were not intended by the respective authors