Question

Hello Rabbi,
In the Talmud, Menachot 79b, Rav Matna said to Rav: “What are the circumstances of this bowl used for the blood? If they hold the blood, we already learned it in the case of one standing; and if they do not hold the blood, then let us say that this is not in accordance with Rabbi Yehuda, for we learned: ‘He stirs and guards it’ — these are the words of Rabbi Yehuda.” He said to him: “I was speaking of a case where they do hold it, and even according to Rabbi Yehuda,” etc. And in Maimonides, Laws of Things Forbidden for the Altar, chapter 3, halakha 11, he rules in accordance with Rabbi Yehuda, and the commentaries there explained that from the fact that Rav made an effort to establish it even according to Rabbi Yehuda, it follows that the Jewish law is in accordance with his view.
But this is difficult for me, because Rav himself in Zevachim 25a said: “Blood that flows out effects atonement” (that is, that gathering the blood into a bowl is not necessary for atonement). If so, Rav contradicts himself. What is the answer?
Thank you very much