Good question, I also have 3% European Jewish in my results and I'm thinking that it's likely just statistical noise or perhaps it was AncestryDNA's way of attempting to categorize my DNA. My actual ancestry hails from Sicily/Italy, British Isles, and a small portion from Alsace (French-German border region). Additionally, I have 14% admixture from West Asia (mostly Caucasus with a bit of Middle East) which I attribute to my Sicilian ancestry, and since Jews are essentially a Mediterranean/Middle Eastern people (with Ashkenazim and Sephardim both possessing varying levels of European admixture), I suspect it may be within that part of my heritage, but there's no way to tell and I'm just speculating.