Glad you found the solution
When dragging images into Hype, if you have
image.jpg and email@example.com, an image group will be created. If you drag one large image (image2.jpg) into Hype, and show it on your scene at 1/2 the size, then Hype will ensure that two version are generated: 1 for retina devices, and 1 for non retina devices.
More info here: http://tumult.com/hype/documentation/3.0/#image-optimization