chm13 is from a "complete hydatidiform mole" https://en.wikipedia.org/wiki/Molar_pregnancy and the paper says "Local ancestry analysis shows that most of the CHM13 genome is of European origin, including regions of Neanderthal introgression, with some predicted admixture" and fig 1 shows a cool breakdown of the regions of the genome with different ancestries

Seems to be an immortalized (telomerase*-transformed) cell line from a female fetus with near-complete homozygosity (https://sites.google.com/ucsc.edu/t2tworkinggroup/chm13-cell...).

* Telomerase is a reverse transcriptase that allows to achieve replicative immortality (https://academic.oup.com/hmg/article/9/3/403/715108).