I think SJ found it natural to just say "OK" because he thought that the person mailing him knew him enough and was mature enough to just need that permission.
As someone outside of Apple, the few times I got replies from SJ were of similar brevity, aside from one, which was a vegan cake that used apple sauce instead of eggs along with directions. I wish I had kept it longer, knowing his fate.
I'm really curious how you ended up getting recipes from Steve Jobs.
From what I've heard from Apple people, terse emails (or just forwards with no additional message) were very common from Steve Jobs.