Re: Ghurids were Pashtuns
Just because they spoke “a language different from that of Khurasan”, it does not imply automatically that they did not speak Persian or Turkish.
Persian was an evolving language that time, from Middle Persian to New Persian. There must have been differences in dialects in different regions, especially in a region like Ghur which was religiously different from its neighbors.
Ghurids are known to have originated from the family whose name is said to have derived from Middle Persian.
From Encyclopedia Iranica:
Ghaurid Dynasty
The Ghurids came from the Sansabani family. The name of the eponym Sansab probably derives from the Middle Persian name Wisnasp (Justi, Namenbuch, p. 282).