Da'at Zekenim on Genesis 7:2

מכל הבהמה הטהורה. פרש"י העתידה להיות טהורה לישראל למדנו שלמד נח תורה ותימה מהא דאמרינן בזבחים פ' פרת חטאת מנא ידע כל שהתיבה קולטתו טהור. וכל שאין התיבה קולטתו טמא אלמא לא ידע אלא מתוך קליטת התבה. ויש מפרשים שאין להוכיח שלמד תורה אלא מדלא הקריב קרבן ביציאתו מן התיבה אלא מן הטהורה. והאי נמי לא נהירא שהרי הבין זה ממה שאמר לו ית' להכניס מהם שבעה. כי כן פירש"י גבי ויקח מכל הבהמה הטהורה אמר נח לא צוה לי הקב"ה להכניס מאלו שבעה אלא כדי להקריב מהן קרבן. לכך נ"ל דמה שלמד נח תורה כדפרש"י. והא דקאמר בזבחים מנא ידע לא קאי אטהורים וטמאים דמזה לא היה מתרץ כלום כל שהתבה קולטתו טהור שהרי התבה קלטה טמאים לכל הפחות שנים מכל אם לא נפרש כל שהתבה קולטתו יותר משנים טהור אלא קאי אקרא דמהעוף למינהו דפרש"י מאותן שדבקו במינן ועל זה פי' מנא ידע נח ומשני כל שהתבה קולטתו טהור פי' שדבקו במינם וכל שאין התבה קולטתו טמא פי' דבקו בשאינן מינן וטהורה וטמאה שייכא גבי ערוה דכתיב אל תטמאו בהם: מכל הבהמה הטהורה, “from all of the ritually pure domestic animals;” seeing that the Torah had not been given yet, and therefore there were no ritually impure domestic animals or creatures, Rashi understands the expression as referring to the domestic animals that would in the future be described as being ritually pure. We therefore learn that Noach had already studied Torah laws which had not yet been revealed publicly (B’reshit Rabbah, 40, based on Psalms 1,2) If so, why did the Talmud in tractate Zevachim folio 116 have to pose the question of how Noach knew, and to answer that the ritually pure animals came to the ark on their own, whereas Noach had to round up the others in order to bring them into the ark? According to the Talmud, Noach only recognised ritually pure animals after the event, not because he had learned the physical signs described in the Torah.
There is a third opinion according to which it became clear which animals had been ritually pure only after Noach offered some of these as offerings after having left the ark. This interpretation is also not logical as G–d had commanded him prior to entering the ark to take seven pairs each of the ritually pure animals into the ark, so that he must have known beforehand which animals to take. This is also what Rashi commented on chapter 8, verse 20. He had realised that the only reason he had been commanded to take seven pairs of the species concerned was in order to have these animals available after the deluge to serves as sacrifices. It would appear therefore that the statement that Noach had studied the Torah, must have referred to the instructions to take such ritually pure birds, (6,4) something which became clear to him when noting that these birds were monogamous, mating only with the same female. When he saw that the ark accepted more than one pair of certain animals, it became clear to him that the extra specimens must have been meant to serve as sacrifices as G–d considered them as ritually pure. “Studying Torah,” as mentioned by Rashi, must mean therefore that he learned Torah by keeping his eyes open and drawing the right conclusions. He had also noted that these animals had only kept company with members of their own species during the long months in the ark. This is most likely also the reason why, when the Torah wrote the details about the laws of chastity and forbidden sexual intercourse in Leviticus 18,23-24, it stated that Jews must not defile themselves through such animals.