Could be flow related, that 75G tank in the picture had a Mag18 return pump and 2 Koralia4's. Lots of flow that blew the mushrooms off the rocks and made them spread all over the tank.
One thing I know is no LFS in my area will take green striped mushrooms because they are considered a "weed" and grow way to fast for them. When my ex-neighbor tore down that tank he brought all the live rock back to the LFS (he offered whatever I wanted first, but not even I wanted rocks infested with mushrooms) hoping to get some sort of credit, at least for the rock, but nope, all the LFS would do it take the rock for free because they were all "infested" with green striped mushrooms, so they made the value of the rock, 120lbs, worth $0/lb with the mushrooms on it. 4/4 LFS wouldn't offer a penny for 120lbs of rock because of the shrooms. All the LFS told him if they were any type of mushroom other than green striped, he could have got some $ for them, but with the green striped all over them it would require too much work for the LFS to clean the rock of them so it wasn't worth the time/energy. Every LFS compared green striped mushrooms to aiptasia and I have to agree, they are just as toxic, spread faster than aiptasia, and just as harmful to other corals they touch as aiptasia. He practically had to beg the LFS he bought the rock from just to take it from him because he had tore down his tank and went through the effort of putting all the rock in rubbermaids to bring back to the LFS and didn't want to have to haul them back home with no tank to put them in.