The fact that Arabs are also a semitic people is a semantic irrelevance. The term 'Antisemitism', by long usage which to any linguist trumps adventitious & factitious etymology, only means prejudice against Jews -- consult any decent dictionary*. The affectation that it must mean Arabs too is a profoundly irritating bit issue-muddying smartarsery.

≈M≈

*eg in online Dictionary.com, the sole definition is

noun
1.
discrimination against or prejudice or hostility toward Jews.