Waters is saying that he is not antisemitic - because Arabs are semites, and therefore it is Israel that is antisemitic, not him.
This is one of the oldest and dumbest arguments in the book. The definition of anti-semitism is in every dictionary, and it is Waters' Palestinian pets who are antisemitic, as is Waters himself based on plenty of evidence.
But no one accused Roger Waters of having a towering intellect.
As usual with this sort of news, Israellycool is all over it.
(h/t Jonathan Hoffman)