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Current thinking says that IVC was formed by Iranian farmers and Southern (ASI) hunter gatherers.
The event you refer to was about after 9000 years ago, when two arms of ancient agriculture spread into India from the west (Iran) and the east (China).
Cheers, Doc
IVC didn't evolve out of a Cultural vaccum. Three distinct phases of development have been documented in the Harappan civilization, this phase of evolution is both cultural, like development of distinct styles of pottery, distinct urban settlement techniques, but also chronological. The early Harappan phase(3200 BCE - 2600 BCE), The mature Harappan phase (2600 BCE - 1900 BCE), The late Harappan phase (1900 BCE - 1300 BCE)
But even in the early Harappan phase agriculture appears to be well developed, which means early phase of development of agriculture in the greater Indus area must be dated to a period before 3200 BCE. The evidence for this early phase of development in agriculture shows up in the Mehrgarh in balochistan. The Mehrgarh site has been occupied since 5500 BCE.
If you couple David Reich's hypothesis that, based on the gene analysis, people from West of the Indus basin came into interaction with South Asian hunter gathers, with Prof Renfrew's model of expansion of Anatolian farming communities spreading their advanced agricultural technology around 7000 BCE, you get this picture of the Mehrgarh phase of the pre-indus core population group. This pre-indus core population, with advanced farming techniques and early urban settlement techniques, then goes on to develop the Indus valley civilization.
This pre-indus population group carries with it the traces of common ancestry with European ancestry, because the same Anatolian farming communities went north towards Europe and Eurasia. This pre-indus population group, or at least part of it, carried with it characteristic of the earliest Indo-European language similar to the ones found in Europe, because the expanding Anatolian farming communities spoke an earlier form of proto-indo European, which then evolved into the mature Indo-European languages of the later period.
This we can explain the shared genetic ancestry, shared language system, without any need for an Aryan invasion in the late bronze age into India. These developments happened in the pre - Aryan people.