Shrug. You can say that for any kingdom. The Germanic concept of a "kingdom" is not a geographic area, it is a political area, defined by folks, not acres.  The area (often a Latin term) will always be an informal shorthand for a collection of dominions of barons owing allegiance to a king. "East Franks" are a folk, "Germany" is an area. "Lombards" are a folk. "Italy" is an area, etc. The "Kingdom of Germany" refers to the collection of barons in the area that once constituted the lands of the East Franks and their subject tribes (Swabians, Bavarians, Saxons, Thuringians, etc.), which by the 10th-11th C. is now settled down into large duchies (the royal duchy of Franconia, plus Swabia, Bavaria, Saxony, etc.).  This specific collection of barons acclaim their king, who is crowned in Aachen (usually) by the Archbishop of Mainz (almost always).  This is the "King of Germany", and the area these barons cover we can call the "Kingdom of Germany".  There really is no term more convenient to call him or it.