Did you read the article? The argument was that tin doesn't occur in many places, so only the powerful even had access to bronze, which was a far superior material, which made it easy to subjugate the vast majority with no access to any material which could rival bronze. Whereas iron is abundant, so everyone has access to it, making it difficult to subjugate other people, because they could fight back.
Completely agree. I wonder how much this varies across cultures on the country level (like how people say the Dutch are blunt).
I think that indirectness emerges when a critical mass of people decide that they're better off in an indirect culture. i.e., thinking "nobody is straightforward with me, but that's worth it because it means I don't have to be straightforward with anyone else". And of course that's infuriating for anyone who would rather take the opposite deal!