He could have said the boy was much loved on this earth, "And therefore we must all trust in God's mercy 'especially for those in most need of Thy mercy', as the traditional prayer says --- and pray for his purification and redemption."
Anything less than proclaiming "he is right now ecstatic and glorious in the presence of God" may have upset some of the congregation, who were understandably upset anyway.
But saying anything that implies "He's better off" causes suicide copycats: a big, BIG problem, especially for adolescents and young adults.
A “traditional” Catholic priest would have at the forefront of his mind the saving of souls. His reasoning would have been along the lines of: “I must warn others against this type of behavior, and by doing so, may discourage someone from following the same path.”
However, in our modern society, and in this context, it was an ill-advised thing to do.