Indeed, they're not one-time pads - they are symmetric authenticators where both sides hold the same seed, and iterate a PRNG or similarly iterable function eve

Indeed, they're not one-time pads - they are symmetric authenticators where both sides hold the same seed, and iterate a PRNG or similarly iterable function every N units of time (say, 30 seconds), to give you the same new output, based on the same starting seed. Think stream cipher output, with an initialisation vector. They are often called OTPs though (i.e. one-time passcodes), just to cause confusion.