Based on? They are hardly the first to call a character 'Stormcaller'. I can think of two different D&D Settings that have a NPC by that name/title, MTG also has a card by that name IIRC, Tood Lockwood has an image with that title and if one goes looking their are probably dozens more... all predating the Bungie one significantly. Of course I could understand if they get their knickers all knotted up, cause this Stormcaller is certified cooler then theirs.