In the last 50 years the only significant anarchist movement was the zapatistas and the rojava. Neither they or your average anarchist activist are particularly fond of Israel's domestic or foreign policies(though Kurdistan rebels do tend to be supported by Israel, it's for regional political reasons) which to downpunxx means they're antisemitic.
As a rule, anarchists deny "Israel's right to exist as a Jewish state" which is a common litmus test for "antisemitism". Considering they deny the right of any state to exist though...
Easy fix though, he's ban evading since his kbin account was already permabanned once (I believe both from this community and .world itself) for this exact shit.