It is the SNP's that Paabo uses in his comparisons of modern human , neanderthal and denisova to distinguish the species genetically and track how they interbred and contributed SNP's to various modern human populations. If it is possible to know that these archaic genomes are not modern humans based on the data then the same can be done with an extant non modern sapiens today. To say bigfoot can't be hiding in the DNA "would" be intellectually dishonest.