I agree with you. I hope there was some consultation with his family before this decision was made. If nothing else, the family should have been able to keep whatever expenses were made in connection with the animal for which he won the award.
Possibly they do not need the money and/or there is some family reason or sentiment for donating to St. Jude’s.
I expect his family is very proud of him, regardless.
St. Jude’s is the patron Saint for lost causes.
So, perhaps there is a deep and serious reason the boy chose that organization to contribute to.