I was rereading the supplements for Narasimhan et. al. for the purposes of trying to adduce the best model to calculate “steppe” proportions in Iranians (someone asked I do this). In the process, I noticed this passage again:
Third, we find that one of the outliers, Bustan_BA_o2, is consistent with being admixed between an individual related to people on the Indus Periphery Cline and Middle to Late Bronze Age Steppe pastoralists, a type of admixture event we also observe in the Late Bronze-Iron Age Swat Valley that we will examine later, suggesting that the admixture events that led to the formation of the SPGT in Pakistan also occurred between outlier individuals at the BMAC and Steppe pastoralists who arrived at the end of the 2nd millennium.
Here is some detail on the site of the sample: UZ-BST-015, Site 4, Grave 4, 57-27 (I11520): Date of 1613-1509 calBCE (3280±20 BP, PSUAMS-4605). The earliest date possible on the Swat samples is 1200 BC (though 1100 BC is more likely). That means that this outlier individual is the earliest example of the genetic mix that would come to characterize much of northern India. A mix of steppe, and Iranian-farmer-related, and Ancient Ancestral South Indian (AASI).
The text of the supplements seems to imply that this individual is sui generis, a mix of Indus Periphery and steppe, which prefigures what was to come later in South Asia. But I will offer another hypothesis: this individual is a migrant, or the child of migrants, from the earliest phase of the ethnogenesis of the Indo-Aryan matrix of Northwest India.