every kind of clean animal: There were animals meant to repopulate the earth. There were also these ceremonially clean animals for food and for Noah's sacrifice after the flood (8:20–21).
This passage does not use the specific terms found in the rules about ceremonially clean and unclean animals given to Israel at Mount Sinai (see Leviticus 11; Deuteronomy 14:3–12). But the basic idea is the same. It could be that God explained it directly to Noah.