That's true at a lot of organizations. The cost of a false positive hire typically vastly outweighs the cost of a false negative, particularly when you have the luxury of being perceived as a premiere employer in the space (from which follows a steady stream of qualified applicants).
I know the rationale. Then again if it's just one 1 person out of 6 (including 3 other persons who gave "very positive" reviews) then maybe that one person is just being ... negative. As the modern interviewing culture (not so subtly) incentivizes them to be.
