I use a microscope this could have been a spawn and the water became too polluted and the coral that started it all was to week from it's spawn it has happened before. I was on a US forum last year and read some thing about coral spawn. I also seen a documentary about corals many years ago that showed corals spawning and it looked just like the photo's. They did say it is pretty rear for it to happen in hobbyist tanks but it could if conditions are right at the right time. Remember these for for the most part wild corals even the cultured ones are wild we just harvest the parts we want. The only way to get true corals that were not wild is to have them spawn in a tank and the spawn grows.

Bill