10th Century Liturgical Abuse?

I checked out a copy of Kenneth Clark's Civilization from the library (that's a story for another time) and in it I found this picture of a carved ivory book from from the 10th century. The subject is clearly the mass being celebrated. Yet it looks very much as if the priest is facing the people rather than ad orientem. Was this sometimes done pre-Trent, or are we essentially seeing a God's-eye-view of the mass in this picture?