In his defense, I only spent 4 (3+ other stuff) years studying Anthropology as a minor, and between visiting excavations, professors, and my personal class experiences, I met a majority of authorities who happened to be Athiests. This may only be my personal experience, but it sure was a lot of them.
Maybe his experience is similar to mine. It does not necessarily represent the larger sample, but it does sway one's thought on the matter.