(a) We find the same Girsa as our Gemara in Yalkut Shimoni 2:852. We find a similar situation, where Rebbi Shimon Bar Yochai challenges a point made by Rebbi Yehoshua Ben Korchah in a matter of Agadah, in Bereishis Rabah 47:1 (see also Yalkut Shimoni 1:256)

(b) Every place I found where Rebbi Yosi is mentioned together with Rebbi Yeshoshua Ben Korchah, the words of Rebbi Yosi precede those of Rebbi Yeshoshua Ben Korchah. It appears that Rebbi Yossi was the greater of the two. (See Megilah 15b, Nedarim 31b, Sanhedrin 19b; in Yerushalmi Sanhedrin 10b we find "Rebbi Yosi and Rebbi Yeshoshua Ben Korchah said," and in Sifra Shemini Parshah 8 we find that Rebbi Yeshoshua Ben Korchah gave Rebbi Yosi special distinction, referring to him as 'Rebbi Yosi b'Ribi'. Rebbi Shimon, on the other hand, was a colleague of RYBK (and we find that his son Rebbi Elazar sat as a Talmid before Rebbi Yeshoshua Ben Korchah - Bava Metzia 84b).

(c) From all the above it appears that the mistake is in our version of Rashi on the Torah (although I did not find a hint of another version, neither there nor in our Sugya, in the Dikdukei Sofrim or in academic versions of Rashi).

With Torah blessings,

Mordecai Kornfeld