Kabol-Ghazna-eastern Hazarajat [that is, eastern afghanistan, where many of Indus' northern tributaries originate from] were frontier mountainous regions, that were much more linked to India than Khorasan, and were populated primarily by Hindus and Budhist tribes, but were conquered by Khorasani Arabs and ruled as attached territories to Khorasan for a long time, as a buffer zone between India and Khorasan. They were not Khorasan either.
Indus was never a river of Khorasan. Its an Indian river. So how can Pakistan be Khorasan? No one is denying that the bulk of the pashtuns are of Khorasani origin, more specifically those in Afghanistan, or even tens of millions of Pakistanis especially Punjabis and Kashmiris. But then so are millions in India, and millions throughout Iran and the rest of the Middle East.
Khorasan includes: 1) North east of Iran including: Beginning in Semnan, to Gurgaan, Sabzvaar, Sarakhs, Mashhad-Neshapour-Toos, Birjand, Qohistan 2) Beloved Afghanistan: Herat, Balkh, Hazarajat, Ghazni-Kabol, Ghor 3) Turkmenistan, Uzbekistan - Marv, Termez As you can see there is no sign of pakistan in here
