Indeed, you can see it is fairly dry over parts of central and western China compared to many other places, such as eastern China and back nearer Europe... due in part to the affects of the mountains and distance from large bodies of water... though you may also notice other spots to the west do show comparable moisture for this date despite producing lower temperatures.

Ground cover differences are part of the reason (more plants = more area the solar energy is distributed into, plus typically store moisture, equating to slower temperature changes).

And then wind direction gives one final explanation why it's not as warm further to the west:

The northerly winds have been in place for a while back in Kazakhstan and Uzbekistan have brought slightly cooler temperatures down from the north, whereas the flow into China is less consistent and has only recently started shifting. Even in the summer, wind changes and even fronts are still often very important in the temperature layout.