I think that some kids pursue an interest or passion for a while and when they sense that the intensity is too much, they like to back off and try other things and go back to the passion later on. The child may have been putting too much pressure on themselves rather than the parent pushing their child - in our family, we need to tell our child to slow down because he pushes himself too much.
So, it is not out of the normal for a child who has been spending a lot of time on one activity to feel that the time has come to explore other activities or hobbies.
I would not abandon chess right now. I suggest that you talk to him about other games/sports/activities that he can pursue over the summer and tell him that we will spend lesser time on chess and maybe explore basketball/soccer/astronomy/dancing/swimming/"whatever you like" this summer.
