The architecture never had a good name. AMD originally called it "x86-64" (but not AFAIK "AMD64", even though lots of other people did), but "x86_64" is most common in the open source world (I guess because the underscore makes it legal as a C symbol). "x64" is what Sun and Microsoft decided to use. Intel has called it "ia32e", "EM64T" and "Intel 64" at various times.
I think this article gets a pass.