The only thing they really changed, was getting away from WW2 shooters, because the market was over saturated with them. I don't believe it was an answer to any competition, but merely recognizing that the series was due for change. The multiplayer stuff taking off the way it did, was a happy accident. Nobody really expected much on that front, from COD4 when it first came out.
With that guy, he's a "PC Master Race" guy, and basically tries to dismiss anything that console games revolutionized. Hence why he's trying to say that COD4's multiplayer blueprint wasn't a big deal and wasn't influential at all, because a game or two before it, had a "reward" system of sorts. Not that it wasn't a PC game as well, but because it blew up on consoles and made it the juggernaut it is today, he has to downgrade it. He also has argued that GTA3 wasn't a revolutionary game that essentially created an entire genre, and it was only popular with edgy teenagers.