The quotes used do not say all UFOs are structured metallic craft. Some UFOs ( within the context that was used ) have been reported to have been glowing spheres of unknown composition that behave like craft, but are neither saucer shaped, nor metallic looking.
Also, try ro keep in mind that the context of the word UFO sometimes references UFOs themselves, and at other times references UFO reports. So it is important ( as with many other words ) to take into account the context. What we seem to be dealing with here is the presumption of UFO reports as opposed to UFOs themselves, as well as the context of informal converstaion with people who are not aware of the official definitions and who simply use the incomplete and misleading term that common dictionaries use. Admittedly these factors can be confusing and in an online forum like this, it's easy to get derailed, but if care is taken to phrase things in their proper context, and confirm once in a while with others that we are all talking about the same thing, then it is still possible to make some progress.