I also used to think that anti-Zionism = anti-Semitism, until I learned more about it. There are plenty of anti-Zionist Jews, both inside and outside Israel. This short clip explains the difference pretty well: https://www.youtube.com/watch?v=u7dJLP3L0Xw
> There are plenty of anti-Zionist Jews, both inside and outside Israel
Yes, Zionism was originally a minority nationalist movement within the Orthodox and Conservative Jewish communities. Only more recently did they become larger, empowered in part for political reasons by other political powers.
There are still large sects of Orthodox Judaism that believe that the existence of Israel actually prevents the Messiah from coming, because the true Israeli state will be founded by the Messiah.
In short: it's complicated. Not all Jews are Xionists, and not a Zionists are Jewish (anti-Semitic white nationalists are actually big supporters of Israel for reasons that aren't too surprising if you think about their motivations and the implications). And the reverse is true in both directions for people who oppose Zionism or the current Israeli state.
Speaking as an anti-zionist Jew, I'm generally extremely suspicious of gentiles who throw the word "zionist" around. Within the Jewish population there's a broad spectrum of opinion between AIPAC and Jewish Voice for Peace. In the mouths of the goyim, though, "zionists" doesn't often mean "supporters of Israeli nationalism". It means "the cabal of hebrews who manipulate world affairs to their own profit." Even though it's not the dictionary definition, that context is inextricable and often deliberate.
For myself, I'm perfectly comfortable with a non-Jew calling themselves anti-Israel. That's just politics. But anti-zionist? Now I'm waiting for the other shoe to drop.