I was just trying to draw a correlation on the source. Up until you posted, in 20 years of reefing, the only time that I saw that particular sponge was from that LR in my tank.
I dont think its something bad though, I am 90% sure that it is the same sponge that I had, which I really enjoyed and never had any problems with (it did grow quickly and I had to remove some of it though) butI never was able to positively identify it as anything but a sponge.
I would enjoy it and be happy that your system can support sponges, besides, it contrasts nicely with your coraline!