1) If you want, you could say that this is an earlier Ravina. Tosfos (Chulin 48a, DH Amar Ravina) writes that it may be that there is an earlier Ravina than the one who was a friend of Rav Ashi. The Shitah Mekubetzes (Nedarim 8b, DH Havah) also writes that the Ravina mentioned there in the Gemara is not the Ravina who is always mentioned together with Rav Ashi.

2) However, I do not know if we need to resort to saying this. We sometimes find that the words of Rav Ashi are rejected by the Gemara. See Pesachim 11a where the Gemara states, "What Rav Ashi said is 'Bedusa' (incorrect)." The Mesores ha'Shas there cites a number of other places where we find something similar. Sometimes the text of the Gemara is "Berusa," with a Reish. The Mesores ha'Shas cites the Aruch who writes that where the Chachamim made a mistake, the Gemara did not want to insult them, so it said that it is "Berusa," an "external opinion."

3) At any rate, we do find sometimes that the Gemara disagrees with Rav Ashi. It is true that Tosfos in Chulin (2b, DH Ana) writes that Rav Ashi arranged the Gemara. However, Rashi in Sukah (end of 3b DH Hayesa) writes that the rulings stated there in the Gemara were said by the members of the yeshivah who were in the Beis Midrash of Rav Ashi, who arranged the Gemara. It seems that some parts of the Gemara may have been written by the students of Rav Ashi. We also know that there are some passages in the Gemara written by the Rabanan Savurai, the sages who lived immediately after the period of the Amora'im.

4) Therefore, it is possible to say that the Gemara itself sometimes is able to disagree also with Ravina, the colleague of Rav Ashi.

Kol Tuv,

Dovid Bloom