This cannot be speaking of Passover because the Passover sacrifice is not selected "from the flock and the herd." It had to be a kid of the goats or a sheep—it could not come from the herd, meaning from cows. Instead, Moses is writing about a sacrifice on the first day of Unleavened Bread.
The word "roast" (KJV) is mistranslated. The word here is bashal, which means "to boil." Was the sacrifice of the Passover allowed to be boiled? No, it was not.