> something different came along and called itself "Perl 6"

You appear to forget that the "Perl 6" initiative originally came from the Perl 5 Porters. It did not just come along and called itself "Perl 6": the "Perl 6" name was used because originally it was intended as the successor of Perl 5.

That it didn't materialize in time, that it became something much different, is something that happened later. But even with Pugs around 2005, Perl 6 was still the successor to Perl 5. Only around 2010, when the sister language concept was introduced, was Perl 6 considered to be a different language.