They are excepted, kind of built-ins.
That is really a huge wart, far worse than general bareword filehandles could ever be. You still have the syntax cases, except now they are special cases instead of instances of a general rule.
And the user you are responding to is pretty unknown here and had only 2 posts so far, so I'd be really careful to rely on such sources.
Duly noted, which is one of the reasons I am in no particular rush: if Perl7 does turn into Perl6 all over again, I am confident that it will end similarly, with Perl5 carrying on.