I don't really know enough about linguistics to be an expert on that exact linguistic difference. However, the map you supplied looks quite similar to the modern separation between the Indo-Iranian branch of Indo-European and the rest. It is believed that Indo-Iranian goes back to about the 3rd Millenium, BC. Their separate recorded history starts around the 9th century BC, when they (and their invention, the chariot) invaded the Iranian plateau. From there some of them turned east and invaded India as well. Presumably this cut them off a bit from the rest of their Indo-European compatriots up on the western Eurasian Steppe, and already "migrating" into Europe.
Note that a lot of the Germanic languages (but not English), according to that map have no dominant order.