tree ting could happen
IMO
bad aclimatation and I woulb be very surprise this was the case here sinc your not a newbe
the fish was about to die and and he do unfotunatly in you tank (go for refun)
your tang have beat him to death. Very possible since tang are sometime realy bad fish depend on there caractere and I have heard a couple of story of yellow and purple killing then realy fast. I have tree tang and no one have even look at mine when I introduce him but some are realy bad guy
sorry