The flying healer (Caladria) was an Atlantean unit, and the catapult (Petrobolos) is Greek. Hippocrates was the new Greek unit and Onager for Atlanteans, which is more of an anti-building siege unit. It can be a bit confusing because in the original game's campaign, the "Atlantean" nation was represented by the Greek civ. And the Atlantean civ did get the Cheiroballista which is a counter-infantry unit technically classified as siege.