I always saw it as god not needing to lie. It makes no sense to imply that god is somehow incapable of deceiving someone or saying something that isn't true. That would actually mean he was limited in some way.
But when you are the incalculably powerful magic overlord of a universe that you created with your own hands, why would you need to lie? Who would he need to fear, that he would try to misdirect them? Who could block him from any thought, word or action? It's not that he is somehow unable to lie, it's just that it wouldn't make sense.