It looks like some aftermarket suppliers/manufactures may have done that for their own personal agenda, such as to profit from it; however, doing so does not make it true. In fact it now adds confusion, especially since we now have a real 6th generation Goldwing.
Here is how wikipedia says it "Some retailers of aftermarket add-ons/replacements parts, group all GL1800 models into two categories. They describe all GL1800s made from 2001-2010 as "First Generation" or "1st Gen,"[97] while GL1800's made in 2012 or 2013 are described as "Second Generation" or "2nd Gen."[98] This is extremely misleading because, in terms of complete Gold Wing evolution, the GL1800 itself is actually the 5th generation."