I would not describe my son as shy, I think he is outgoing but in certain times, when in a new situation, he would suddenly shift to being shy.
If in a new surrounding and when we kinda force him to interact he would go in his ‘shell’ and hide a bit. He sometimes look down, hide behind our legs, or look away and ignore everyone. This would last for about a few minutes but after getting used to the surroundings he would relax and be normal in his old wild, exuberant ways.
The world is not made for shy people, it is for socialable people and being an extrovert brings tons of advantages and it is a trait that I hope he would happily embrace.