I agree with Natascha's evaluation of the "masters" bit. When they featured my work, not for one minute did I think they really thought I was a master of anything. It was more like "hey, neat video." I personally do not follow them because they feature work of many calligraphers that I follow, and although discovering new talent is nice, I dislike seeing duplicate posts in my feed (picky picky!).
Do I think that that group is in a position to judge our talents? No. Are they actually trying to put themselves in that position? I don't really think so. I think they're just sharing work that they admire.
Overall, I think it's pretty clear that this has nothing to do with, nor is it trying to have anything to do with the "Master Calligrapher" title (although, perhaps a word more humble than "master" would be more appropriate, so I agree with Salman there). Also, regarding anyone who tries to attack someone whose work is featured on a feed just because it has the word "master" in it, well, shame on them.