If the white was cottony, it was 99.9% chance of a fungus. I'm not experienced with corals and fungus, but I did have a fungus infection on fish and it was easily cured with an antibac. If the other corals look healthy they more than likely will be fine and no harm done.
It's a shame that you had to toss those corals. But the people that replied to you were experienced coral keepers. Can anyone explain why he couldn't just do a dip and/or a antibotic treatment in a seperate QT?