There is a vast difference between wartime alert and peacetime alert. To date, the US has no reason to regard China as a 21st century adversary al la the Soviet Union. I'd suggest that attitudes are changing though. Personally I question some of the decisions made by prev CINCPAC and current CINCPAC. If it walks like a duck, quacks like a duck, then ipso facto....But what about in peacetime? This would be significant in explaining why that sub got so close (for those who bevlieve this somehow show the vulnerablility of a CBG to chinese SSN's). The grid was not up and running becasue the USN was not going to expend $4500 for a 10 boey patern in peace time.
It's the same scenario as Russian overflights, anyone with half a brain will realise that a russian overflight signifies no threat - and why respond anyway unless relationships really deterioriate. At that point the entire posture will change. Ditto for a chinese sub surfacing close to a CTF. The PLAN have done the same with Talisman Sabre. Do we go mad and send out frigates madly dropping hoovers everywhere? nope. we listen, they listen. big deal.
Although, I'd suggest that patience and goodwill is running out....