It's probably not helped by the fact that he does empty, tedious storylines that are far more concerned with style than substance, and is an ass about his mediocrity.
In 2006 he made Lady in the Water which unquestionably has a twist ending. The Happening might not have a twist in the traditional sense, but surely the "surprise" of it is very Shyamalan.
A plot twist is when a road you were led down, story-wise, turns out to be a false one and the real road is something else. Hence, the ending of Lady is definitely a twist. Everything you were led to believe is reversed and/or altered in a sudden, last minute sort of way.