MP stands for 'Multiplayer', Co-op is a form of Multiplayer. And even then, they never said it would be co-op, just that they were working on online compontents when asked about multiplayer:
I really don't think - or hope - assualt rifles will make it to the game. Ammo is scarce and assualt rifles would ruin the idea
im guessing the riffle will be the sniper of the game
Well, first of all, there could be more ranged weapons, this could of been only some of them because they released this gameplay in 2012 and the game is to be released in 2013. Anyway the showed the Cocktail Molotove which I guess could be considered a ranged weapon also.
(I know It says rifles but I wanna make a point and this is assualt rifles.)I think there will be Assualt rifles. Im pretty sure about it. If you watch naughtydog's The Last Of Us presentation, right after Joel takes care of the infected, you can see Ellie carrying a gun which I believe is a AK, which then Joel takes from her. Knowing that from the presentation I think there will be Assualt rifles.
Heres the link to the presentation if you wanna check it out: (You see Ellie carrying it at just about 3:20)