It seems odd that the U.S Military is not in control of Tashgar but think about it. They have been holding the area for god knows how long and the Russian army is really frigging big, not to mention that the AA has been destroying their planes. Adding to this, replay the opening of the level and take a good long look: there are allied tanks and Russian BTR's in smoking wrecks. No doubt a fight broke out and they had to pull back to the (at the time) safety of the airfield. It was only when the Chinese rolled in that they fled to Old Town. And thus, you are late to the party, having to fight through the reinforcements.
The AK-12 may seems like a Unintentional Period Piece but it actually make sense considering that US and Russia went to war in 2014 and Sergey Urzhumcev's design is from 2015, is likely that either Russia adopted Zlobin's design to get a modern weapon quickly or Urzhumcev may have died in the conflict.
Fridge Logic
Chinese spec ops in Shanghai, invading a peaceful city, and no one thinks to inform the home guard? Granted, Siege of Shanghai clears it up (the U.S moves in to remove China from Shanghai) but still, kind of a stupid move.
Fridge Horror
The Final Stand DLC confirms that the game is set in the same universe as Battlefield 2142, which means that the second ice age that wipes out almost all life on Earth through cold and starvation is inevitable.
