Wrathful red dragon and blasphemous act

I was in a game of commander. I cast the blasphemous act with 8 dragons in total. One of my opponents noticed that I have wrathful red dragon on the feild. Before they pass priority they ask where the triggered targeted damages would go. I ask them if the blasphemous resolves because I wasn't going to reveal that until they trigger. They tell me that I have to tell them the targets so that they could properly make decisions which i know about. I tell them said triggers haven't triggered until the damage is dealt. The whole table starts telling me that I'm wrong and that wrathful red dragon is seeing the damage from the spell and is already assigning the targets. I'm forced to leave before anything else happens due to cheating.

Who was right?