The genome of Denisova 11 was sequenced at what researchers call medium to high coverage — sufficient to carry out the detailed analyses of ancestry proportion, chromosomal identity, and specific variant comparison that produced the extraordinary result.

The quality of the data was high enough that researchers could confidently assign individual chromosomes to their parental origin — distinguishing the Neanderthal chromosome from its Denisovan partner at each position in the genome.

This level of precision — the ability not just to say that someone had ancestry from two different groups but to identify specifically which chromosomes came from which group and trace specific genetic variants back to their parental origin — is what made the Denisova 11 finding so definitive.

It was not a statistical inference.