What are you guys talking about? Its a summer pic. No one is wearing any seriously warm clothes. They are all dressed the same.
Of course it never is really warm up there. But during the summers if the wind catches up or when the sun goes down it gets cold enough to wear 3 layers. At 3800 meters in the summers a little sun light without wind can make you sweat if you exert your self. But without a moments notice the wind can pick up and you can get ill, even with a breeze if your not prepared. Btw anyone who has ever been up there will always take the climate there very seriously. Any one showing off up there is only an idiot and nothing more. Even the locals there dont take the climate easily at any time of the year. And the guys in the pic would surely know what they are doing.
ps: The winters are a VERY different ball game all together.