If I'm right then we might have to rework that theory. Even Kashmiri, some speak dialects which are more similar to Persian. Like Burushaski.
It is well established that Odḍḍiyāna was well within the Indo-cultural sphere. We have many reports of Chinese pilgrims going through it and so on.
As far as Burushaki goes:Although Burushaski has been compared to almost any language on earth, no fully convincing relationships have yet been established.http://dickgrune.com/NatLang/Summaries/Burushaski.pdf
While this document claims that no written Burushaki language exists, it is claimed that Nubchen translated the Anuyoga tantras from this language, and in fact Burushaki words do exist in the Anuyoga tantras.
But there is no relationship here with Persian.
I just watched this doc about this old tribe in Pakistan, near the Swat, the Kalash tribe (among others). These Aryan tribals were more numerous back then. I would argue, the Chinese accounts of Oddiyana, i.e., their infatuation with mantric formula, is decidedly Zoro... in influence. I see culture as spectral. In this area you have a blend of both the Proto-Aryan, Persian and Indian in the Swat and around Afghanistan, Turkmenistan, Uzbekistan, Kyrgistan, etc... This whole area was under heavy historical influence by Persia, India and China... It would be difficult to pigeon-hole Swat as "culturally Indian." Then, as now, it had its distinct idiosyncrasies that made it seem a little far North of Indian.