Unlike the other things, this is not surprising. Zionism is, necessarily, a movement that accepts no compromise about one people moving into a space presently occupied by another. Yes, it's the Jews' ancestral homeland. But it is also the ancestral homeland of Islamic peoples (more recently, but not for as long). And yes, it's complicated, because Jews have always lived in that region, but not in sufficient numbers (in recent centuries) to control it...and yes, it's even more complicated because presently there's a mix of displacement (e.g. in Jerusalem) and creation of new dwellings from essentially unoccupied are (e.g. Tel Aviv). And this hardly scratches the surface of the issues. However, despite all the complexity, "don't displace people against their will through force" is absolutely a core leftist belief, and "I am a leftist except I have this giant gaping exception for anything right-wing Israeli politicians might choose to do" might very well be a deal-breaker for a lot of leftists.

So although it's not clearly required to be anti-Zionist if you're a leftist, it's also entirely consistent for a leftist to be a pragmatic anti-Zionist. (It's a bit harder in principle, given that freedom of place to live is generally consistent with leftist ideals--it's just that if someone does not grant you that freedom, forcing the issue is not, generally, considered to be okay.)

Now, it's entirely plausible that people write "no Zionists" when they mean "no Jews". That's disingenuous...but...the Zionists are also not being entirely forthright when they conflate opposition to Israel's policies of occupation to anti-Semitism. Quite a mess.

None of it excuses anti-Semitism in the least, though, nor does it excuse erasing Jewish contributions in all sorts of areas, including very notably in humane treatment of people of color in the United States.

It is rather depressing that some of the worst offenders are those who call most loudly for solidarity and for their own group's contributions to not be erased.