It all depends, sometimes its random when fish get into confrontation. I have a buddy who had a goliath and a armatus together for sometime and then all of a sudden one wipe out the other.
Ive never understood putting rays and aro together TBH. They might look good but one cost a fortune, the other cost a fortune and has a stinger on it to boot. Cool look but it's always going to be risky.
Sorry the fish died.