Like you said, language evolves. People are deciding that the definition you follow is very limited and constrains dialogue by being needlessly exclusionary. So they’re seeking to expand the definition to its logical conclusion.
You can throw a fit about other Semitic people being recognized or you can accept that language changes to fit our current understanding of the world.
Antisemitism still refers to prejudice against Jewish people. It’s also being extended to all Semitic people as to disallow them the ability to categorize prejudice against them is to obfuscate and to an extent even deny their own reality.