Yes, I know I don’t have any basis in fact for that guess, but it just sounds so perfect a theory - “oh people spread across the littoral”.
It would be nice to have more written records (such as a Harappan script decipherment that everyone could live with) but it seems likely that there was one 'coat of paint' after another throughout lower and Central Asia, just as there has been everywhere else on Earth (apart from Antarctica, unless you're Rand Flem-Ath ;^).