Why is this area colder than the surrounding hotter area?
The Himalayas and the Tibetan Plateau have high elevation and temperature drops with altitude up until the tropopause. The temperature on the map is measured and modeled on the land surface, regardless of elevation. You can also see that the temperatures in e.g. Ethiopia and the Caucasus Mountains are lower than surrounding lowlands. 

At latitudes around 30 degrees (north and south), the air is dry and hot due to global circulation pattern. The weather patterns are also controlled by the topography, humid air can't pass the mountain range as it's forced to an altitude where the temperature force it to condensate. That is why the Gobi desert is hot and warm in the summer. 

I hope this answers your question.