Never be alarmed by one start, unless of course there is an injury that occurs. He is not the prospect he is today cause of any one outing, it's what he did in the minors over the course of last year that has people thinking highly of him. That said it shows what a young pitcher he is and that unless you have control of the strike zone, you will get hit even w/ a high 90's FB. I would of let him pitch in AAA and get more seasoning in, but the Tigers keep showing that they aren't willing to do that with their young pitching.
I'm personally not as high as most are on him, but I do think if he stays healthy he could become a potentially nice pitcher w/ a good amount of K's.