Yes, because it’s inconceivable that the leader of an anti-Semitic group which hates Jews, and has a charter which encourages violence against Jews, could make a comment which hates Jews.
If Sinwar has been libelled he is free to take up action. Do you want to bet that he does? I don’t think he would, somehow.
Just because it comes from a source you dislike it doesn’t infer that what he’s saying is false. What next? We can’t quote The Guardian or Right Wing Watch if it has a quote from a right winger, because of the source’s bias? What ridiculousness and it’s telling of the state of the left when it comes to this issue that every disgusting comment made by some anti-Semitic loon is waved off if it comes from a Jewish source. God forbid recognising that there are some very problematic members in Palestinian society.