Well, this reminds me a of a deer we got this year... luckilly... very luckilly.
The young hunter was sitting on the edge of a field when a small doe came out. We had a doe tag, and as such told her to take whatever she saw since she had never taken any big game animal, though she has been hunting with us for years.
Well, the first shot missed completely due to being so excited. The second shot however, connected. When examining the area, I did notice a bizarre spray pattern behind the point of impact. It was quite odd, though quite large. We found small drops of blood heading into the woods... dark spots. About 10 yards in, there was a big smear on the the ground, maybe 12 inches long by 4 inches wide, obvioulsy she had stumbled there. And then... the blood REALLY went dry. We found bits of bone, so we knew for sure is was a solid hit, we thought they were more than likely rib bones. As we progressed, we found only very scarce drops, maybe 20 yards apart. It was dark so we resumed the next day. I must admit, the lack of blood made me very unsure of a fatal hot, however the bone pieces gave us hope.
The next morning we resumed the search. It took us about an hour to find anything at all due to the morning condesation. At last we found a single solitary drop. And as the day before, we searched long and hard to find single drops, maybe 20 to 30 yards apart. Sometimes we got lucky and were able to make out the direction of travel. Many times we had to start over at our last known point.
At this point we had travelled about 400 yards, and the blood started to get a little more frequent. Finally after hours of searching, and almost giving up, we found the doe... dead. She had travelled almost 500 yards, with an absolutely demolished shoulder, but other than that, no vital damage. I was amazed she made it that far considering the trauma to her front. Her front leg was hanging on by a few inches of skin.
Im not quite sure what the cause of death was... we never found that much blood, but there was quite a bit of internal bleeding, so I suppose it was due to that.
All this to say that you have to put in a hell of alot of effort to find a poorly hit animal. The blood spray you mentioned is almost identical to what I saw, and the lack of blood is also identical. I would think your buddy had kinda the same hit, and odds are, the moose went down a considerable distance from the shot.
Here's a photo to illustrate...