I know the sort of account you mean, but I can’t pin that particular Iran story down reliably yet.
There is a well-established older “wild man” tradition running through Iran, the Caucasus, Central Asia and Afghanistan. Early-20th-century accounts collected by Russian zoologist Vitaly Khakhlov describe hairy, humanlike beings in the Iran–Central Asia mountain belt; one account from the Iran-Kabirg region describes herders actually capturing a short, hairy “wild man” with unusually long arms and very humanlike hands and feet. citeturn958889search0turn996588search5
There’s also a genuinely weird historical coincidence: anthropologist Carleton Coon excavated caves in Iran and Afghanistan and later became an outspoken believer that relic populations of humanlike “wild men” could still exist. citeturn958889search45
But I’m not finding a solid source for the specific episode you remember — an isolated primitive group encountering modern Iranians and one of them driving or throwing a spear through an Iranian’s chest. That may be buried in an older cryptozoology book rather than indexed online, or one detail may have migrated from another story.
One possibility I’d keep in mind: Irian Jaya — the former name commonly used for western New Guinea — sounds very much like “Iran” in a decades-old memory, and that region has numerous contact stories involving previously isolated peoples armed with spears. I’m not saying that’s definitely it, just that the phonetic resemblance plus the “isolated primitive tribe” detail makes it worth checking.
And importantly, I wouldn’t merge it with the Kandahar Giant yet. Kandahar already contains the spear-through-the-soldier element, so later retellings could easily have cross-pollinated the stories.
If we do the giants/wild-men Skeptic Desk properly, I think we should build a chronological source table. That will tell us very quickly which creepy similarities existed independently and which ones appeared only after these stories started circulating together.
