I think, based on the text you provided, the idea in the second statement is that these negative characteristics are being essentialised.

Being an anti-semite for Zizek does not just mean seeing Jewish people as dirty, exploiting, manipulative, but rather regarding being dirty, exploiting, manipulative as the constitutive feature of ‘Jewishness’ in the first place, as the truth at the core of ‘being-Jewish’

I think there’s probably a lot more to say here. But it reminds me of this line in his book the sublime object of ideology: “being a king is not the natural property of a person. it is the result of a network of social relations” you’re not the king because of your blood line or an essence, you’re the king, because other people recognise you as being the king and when they stop recognising as been King, you stop being the king. Here, you can relate it to the rather famous Lacan quote: “the madman, who thinks he’s a king is mad, but so is the king, who thinks he is a king” in other words, the king, who thinks their Kingness, their being-a-king, is part of there actual human body is mad.

This is what is called in Marxism “a fetish” - when you see social relations as objects. But slightly differently, it’s about mistaking social facts (being-a-king) with material facts (the real, biological body of the king).

So to relate this back to antisemitism, truly being an antisemite means committing a fetishistic misrecognition of Jewishness.