In startups it's extremely common to have management still write code. Hell I'm CTO and I write a lot of code.
There's a danger in it too because (whether it should or not) CTO title carries a level of weight that might result in less scrutiny than an IC (which it should not IMHO). I hope he is encouraging objective reviews and not pushing stuff through on his title.
In that case I guess you just keep pressing them to document/make notes. Keep asking questions. Basically take away their “saved time” by dumping the time sink they dumped on you back on them.