Aveline, I so agree with you:
sometimes it's necessary to learn appropriate neurotypical skills as a necessary way to get on in life.
Autism should not be used as an excuse for poor behaviour and simple social skills can be learned and used because they frequently do not come naturally.
If this boy has always been like this it sounds as though the parents aren't bothered about his lack of social skills, which they could have instilled from an early age, particularly with a close and familiar, family member. The fact that autism hasn't been mentioned sounds as though he does not have, and may not require a diagnosis; he is simply ill-mannered.
Make a point of greeting him when you arrive and say goodbye to him, and try to exchange a few words; if he pointedly ignores you then consider whether or not you wish to give him a present (personally I would continue until he is an eighteen, then stop and tell him why.)
The fact that his parents let it be known an expensive present is required sounds rather yobbish behaviour.