Adding emphasis:
The new study, conducted by two Harvard researchers at the Institute for Family Studies, found that the original 2020 study “did not control for the impact of very low birth weights (i.e., under 1,500 g) on newborn mortality.”
“Although these types of births are rare, they occur more frequently in the Black population, and they account for a very high fraction of mortality,” the Harvard team found.
Failing to control for a significant factor like this is either very sloppy or knowingly and intentionally skewing the outcome. Modern "research" is often sloppy, and sometimes data is selected or skewed to produce a pre-determined outcome, so I won't try to guess whether the original study was sloppily done or conducted to produce a pre-determined outcome.