Even if someone were unfairly anti-Israel, why would that imply they’re also antisemitic?

Well because it's a Jewish country. And one of the only countries in the world threatened with annihilation by some of its neighbors. When 77 years ago Jews were indeed being exterminated all over the world. This very unique situation warrants someone to at least be careful with the tone and choice of words he uses when criticizing Israel.

If he is not being malinformed, what other reason does he have to spread lies about Israel?

Can residents of Gaza and the occupied West Bank vote in Israeli elections, when they are under Israeli rule? If the answer is no, then that's apartheid.

You're not making the Israeli-Palestinian Conflict better. You're making the word "apartheid" meaningless.

Do they want to vote in Israeli election? Do they even want to live in a democracy, let alone in a binational country together with Israelis?

That is occupation for you. Could residents in Iraq and Afghanistan vote in American elections, when they were under American rule?

Can they vote in their own local government (Hamas and Fatah)? If no (it is) does that make them apartheid?

Double standards or ignorance.