I'm sure it's known but, I don't know.
I think some where along the line they said he had an element (arsenic?) in his hair and they thought he may have been involved in copper working. They assumed the copper was local.
I haven't heard anything about the flint but it was thought to be highly traded commodity so I doubt that would pinpoint his origins.
I was under the impression that Italy got him based on where he was found but also the vegitation found on him and in him were from the south. This sounds like further evidence to support Italy's claim.