I always thought to say that it seems that animals before the mabul were of higher intelligence than the animals after the mabul (for example, the Nachash by the Eitz HaDaas, the issue of eating animals before the mabul, and the fact that they were meZaveg with other minim).
Therefore at this last time before the animals went into the teivah, the Torah calls them Ish VeIshto, to denote the final point when animals were on this higher level.
Maybe there was even a concept of “ish VeIsha” among animals before the mabul?