The ending was a clusterfuck. Nobody knew what to do. Blood in and of itself is no reason to end a match, and Randy's injury, while ugly as hell, was quite clearly in need of treatment. There are medical guidelines that doctors must obey in sports, and I can guarantee you that when somebody has that big of a gash, they simply will not be okayed to continue i.e. WRESTLE. Brock certainly could jump on him a couple of times and flail at his arms, but Randy standing up and doing moves was out of the question at that point. This is the point where I think that shit happened on the fly. Watch the tape - the referee never calls for the bell. That was likely radioed from the back, either from Vince or Trips, who were in the ears of every official in and around that ring. Seriously - that ring was damn near the bastard child of a deer in the headlights and a headless chicken for several minutes until the bell was called for.
Now Shane coming out and getting F5ed was likely the plan from the get-go, but even that was questionable. It's just as believable that Vince said/yelled "DAMN IT, WE HAVE NO ENDING NOW! Shane - go eat an F5" when faced with the chaos and lack of a satisfactory closing that his second biggest show of the year had devolved into.
I'm not saying Randy want supposed to bleed and I'm not saying that Shane wasn't supposed to be F5ed, but I am saying that what actually ended up happening wasn't HOW it was supposed to happen.