Thanks for the query.
There is nothing called as sun poisoning
Sun burn is a common condition.
Dont worry its just a reaction, he will soon recover.
Tell him to take some antihistamine and apply a mild steroid
cream in night and in day use sun screen.
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.
If the condition persists even after the use of cream, please meet a dermatologist