He has Gray going #1 to the Astros with Appel going to the Cubs. This is the second mock draft that I've seen where Gray goes #1. The logic is that Gray will sign for less than Appel and the Astors could then apply that savings to the rest of the draft.
Personally, I find that logic to be a bit suspect. Most scouting reports have Appel and Gray as the #1 and #1A prospects. I'm not sure why Gray would be giving much of a discount over Appel. They are rated just about the same, with Appel being maybe a bit more polished.
Regardless, I'd be happy if it turned out this way.