Sounds like the kid went "berserk" on you. D'you have the relevant announcement log?
It just said tantrum but it did change his name also. When a Dwarf shows up I give them a custom name based on gender, their marriage status, and which migrant wave they are. So it ends up looking like this "SM-1013 NAME". When it became a "@" he went back to his original name - as if he had lost citizenship. But when I checked his dead body in the coffin he had his post-arrival custom name again. I really wish I have taken a image. It was like he was no longer part of the settlement and had become an invader for the time it took them to kill him.
Yeah that sounds like they flipped their shit and went crazy. Tantrums usually preface some manner of insanity and if the tile changed, they were either a werecreature (which doesn't appear to be the case,) or went berserk.
Civies dogpiled them due to the insane numerical advantage and/or a desire to fight, do something exciting, or help whoever went after the berserking dorf first, and now things are going to hell in a handbasket cause they had to see the corpse of a citizen.
EDIT: I just watched a wrestler take down a giant. Not an armed dude marked as a wrestler, but an honest to gods unarmed combat specialist I had (uncreatively) named Fist, since she had those skills but none in a weapon when she first came to Fireblade.
Not weighed down with a shield or weapon, she quickly ran the beast down as it chased some stray cattle around and with a single kick, knocked it unconscious. Before anyone could even catch up to steal her glory, First punched it in the head so hard its head exploded.
Edem "The Fist" Bustcleaned, has been bestowed the custom profession of "Giant Slayer" in honor of this tremendous accomplishment without a weapon.