[zeestephen]

Re: “They knew about the Kennewick man error fairly soon after discovery.”

I agree that the age of the bones was resolved almost immediately.

The major issue was the origin of the bones - Europe or Siberia - which would have challenged the Siberian Land Bridge theory.

My recollection was that no DNA could be extracted because the bones were in wet sand for thousands of years.

[Varda]

The original forensic anthropologist thought they were recent bones. That's why he made the error. He had no expertise in ancient bones and didn't know what he was looking at.

As soon as they knew the bones were ancient they sent them for a detailed examination which came up with no affiliation with any modern people but the closest affiliation was with a southeast Asian group. That and the age and the rest of the find placed them in the paleo-indian group.
The recent DNA test merely confirmed all the other evidence.