I thought that Perl 6 will largely be written in Perl 6, allowing the base that needs to be implemented natively be as small as possible.

Furthermore I heard that there will be multiple implementations of that base, including ones in C, C#, and the JVM. (Or at least that is a pipe dream that people had at one point.)

Even if the most commonly used implementation of Perl 6 was written in C, this would make it true in spirit and fact that the overall language is not written in C any more.