All ability names in Warlock are based on platonism.
Boomerang is named boomerang because of all physical objects it is closest associated with a boomerang
This applies to any abilities: Lightning, Homing, Fire Spray, Splitter, Meteor, Link, etc.
Phantasm does not associate with any property of a physical object and was therefore renamed Arc since the ability inherits in particular the movement pattern of an arc.