It isn't cut and dry.
iPhone 4 and 5/5S had retina non HD because they were 326ppi but not HD (1280x720). The Macs got retina and were well over HD, still called retina though. The iPhones finally went over HD so they are now Retina HD. I read there is some other technology built into the iPhone displays too like dual domain pixels. Now the iMac 27" has retina 5K. So it is somewhat convoluted.