One possibility is that, given the number of Jewish slave owners, it is likely that a significant fraction of those who were descended from colonial-era slaves also have some Jewish patrilineal blood. This could be where the urge to claim Israelite ancestry comes from.
Where they get it totally wrong is that, instead of acknowledging the above, they try to claim that all "blacks" are Israelites. This is why the first thing we need to do is discredit the category "black" to begin with. This would not stop the Jewish blood memory among those who currently self-identify as "black", but it would at least force those among them who want to claim Israelite ancestry to at least attribute their Israelite ancestry to colonial-era Jewish slave owners. But I am quite sure that Jews would prefer their history as colonial-era slave owners not to be brought up. Which is why Jews promotes the notion of "blackness".