While I've met his father (and he's a really nice guy!) and him, I don't know what they told the scouts regarding his signability. I saw him pitch 2 or 3 times this year and I thought he was excellent. I also saw scouts at one of his games so they undoubtedly know about him.
There are a lot of factors that go into the draft. Signability, projection and more. While he is an excellent pitcher, perhaps the scouts felt he needed 3-4 more years at SCU to be "ready." Or, perhaps he said he wouldn't sign no matter what? Thats only a guess on my part as I am not qualified to evaluate him nor do I know what he/his family told the scouts.
In any case, I'm really looking forward to watching him at SCU and hope he has a great career there. I know the coaches at SCU are very happy to have him.