If the language is renamed from its original prototype name of NB meaning New B then it's entirely possible that the very first C compiler was written in C. Remember, with the now extensive differences between B and C, DMR decided it was time for a new name. So if what defines C, specifically the types etc, existed in the NB compiler at the time that NB was renamed to C, then there is no logical problem with saying that the first C compiler was written in C, because it was all originally NB/New B, and just renamed.

Anyway as I said I think only DMR can answer this question definitively. Maybe I should ask him...