All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is not beneficial to think about the identity of the army who will bring victory to Al-Mahdi and think about which race they are. Rather it is more appropriate for a Muslim to think about how to support the Religion of Allaah wherever he is and at any time, as this is the responsibility of the nation at all times. Among the most important factors by which the nation would gain (or regain) victory is by returning to its religion and acting according to the Law of Allaah in all aspects of life and seek help from Allaah.
We are not aware whether or not the origin of the Pathans is from the children of Israel; it is enough to say that they are Muslim people.
With regard to the narrations which state that the people of the black flag are from Khurasaan; some scholars spoke about it, and it is a confirmed fact that this army will be from the children of Is-Haaq. Imaam Muslim reported this in a narration that is mentioned in Fatwa 82172 which you referred to in your question.
An-Nawawi when interpreting the narration, said quoting Al-Qaadhi 'Iyaadh : “All the narrations reported by Imaam Muslim state that they are from the children of Is-Haaq. Some of them [scholars] said that they are from “the children of Ismaa’eel”, as the context of the narration suggests, because it is the Arabs who are intended in the narration”. This means that the narrations did not all agree that these people are from the children of Is-Haaq.
To conclude, saying that the army of Al-Mahdi will be from certain people is of no benefit as we already mentioned, because this army could be composed from groups from different people, and what is mentioned in the narration is the predominant view. However, it is more appropriate for a Muslim to be concerned about what benefits him in this worldly life and in the Hereafter.
Allaah Knows best.