[mrkstu]

Why is that a safe assumption?

You're assuming that he wasn't, in fact, the best candidate that interviewed based on what?

Since they didn't seriously consider him they may have left behind the best candidate available to them. The original poster said "he's one of the most knowledgeable people I've been around."

Assuming that poster has a wide exposure to developers, its highly possible that the position didn't get a better applicant.