Evidence indicates that the guy was not that smart. If he had developed anything, he would have been able to reproduce it, learning from the mistakes they was made the first time.
Look him up on LinkedIn. He's not what I would call "not a smart guy". I'm really, really curious what makes someone with 7 years of work as a senior at Apple go ahead and do such a thing as leaving on bad terms taking his work with him. Not weird, no? At least he didn't end up like a certain unfortunate someone who worked for Sam Altman not long ago.