Yes it does look from the same family as the pictures on the link, especially Actinodendron Plumosun, but their picture is not so good. Mine as probably more than 60 tentacles, of various sizes and is very agile...
I've seen some really large ones in the past, some which have taken up almost half a 20gal tank. They also pack a pretty powerful sting. A large one touched my arm for about 5 sec and left it all blistered.
Looks clearly from the Branching anemones family, the closest being Actinodendron Plumosun...not quite that but haven't found a closer picture on the web...