I believe they knew the clean and unclean food designations and didn't eat unclean. For example:
Gen 7:2 Of every clean beast thou shalt take to thee by sevens, the male and his female: and of beasts that are not clean by two, the male and his female.
If by "kosher" you mean the traditions and rules built up by the Jewish religion over time then probably not.
Thank you. I have a couple of good ones for you concerning Rabbinic kasrut.
When Yitzak was in the tent, Esu went hunting to bring him meat. You cannot shecht a deer with an arrow or a spear.
Avraham served the shalosh hanalachim hema v basar (butter and meat)
Al tevashel gedi ba HALAV emo (do not cook a kid in it’s mother’s milk) could also read, HELEV emo (womb of the mother)
It is forbidden to eat the egg and the hen. However today it is very possible to eat the egg and the hen. How could you know?
Anyway, just a few for your consideration.
Thanks again