Why prompting on reset for icloud account

My son has an old ipad and doesn't recall the passcode. We reset and update through itunes. Now it's prompting for the icloud account that was used to set it up or the passcode (which if we knew, we wouldn't be doing this) because it says "Find my iphone" was set up. When we look in our icloud accounts, this ipad isn't listed. Isn't the whole point of the reset because we don't remember this information? The option listed is to find the person who set it up, who is us... Is there a way to reset it completely?