That's a great looking clam, it is not suffering from the pinching disease. It's completely healthy. What you are seeing is Insane extension mixed with water flow. If the clam was suffering from the piching disease it would not be as vibrant.
Also if it was the pinching disease, then the tiny little maxima on the right side would perish 50 times quicker then the mighty squamosa, which usually are not even effected by it.
I will agree with project reef on the water flow. If you watch the video on the German website, you see a colt coral in the background that is whipping around like crazy and the chromis are getting shuffled pretty well too. Everything else is sps so that is the only signs of ridiculously high current. Assuming that clamis in the same tank of course.
Where do they get the clams anyway?
Project Reef you are connected, got any ideas?