I think it was mainly the show ran way too long. It was almost 4 hours, and I'm guessing their absolute latest they were allowed to run was til midnight ET. By the time they took the stage, there was only maybe 10 minutes left of the show, but you have to factor in about 2 minutes of credits, sponsor shout-outs, etc.
So basically they put them on stage with maybe 5 minutes of actual air time to play what is traditionally a pretty long closing number. Plus how they did it, cutting away to a crowd shot (which showed they were ushering people out too) didn't help.
While I think the Grammys are now silly and a shell of what they used to be, being given the closing act is still considered a pretty big deal, and to then have it hardly shown, I can see why he's upset.
