A miser who happened to be Jewish can conform to a stereotype of a miser even if there aren't any other misers who happen to be Jewish, and people don't think of Jews as misers (quite the revrse actually, I'd say). There's no suggestion that Scrooge, or all the other misers in literature, were Jewish.

Of course it'd be perfectly possible to have a miser who didn't conform to the general stereotype of misers, who are thought of as being crabby and unsocial. I mean, you could have a cheerful and affable miser. Actually Fagin is quite like that - not a stereotype miser at all, really.