Now I will not Justify this Raid leaders actions but having been a Guild Leader and raid leader since Vanilla, I know I have some mods that check what items are best suited to what class and spec's, and we had guild rules for Priority order.

Due to health reasons I haven't really raided since dual spec got fixed. SO I don't know how that plays with the mods.

But the Raid leader having invited and asked your son to play Holy should have known and either payed more attention passing loot or IMHO "he took it because he was perturbed that your son wouldn't switch to holy for the run and thus was determined to try and keep your son from getting gear"