Compared to previous and successor presidents Carter had a pro-Arab policy. This is apparent in his post presidential activism as well. The Iran hostage crisis was fresh and had a lot to do with it. Mondale was quite pro-Israel in the campaign and Ferraro had a good track record in her district.
I obviously know that Carter was/is very pro-Arab after his Presidency, but was he really that pro-Arab during his Presidency? I don't seem to recall that he pushed Israel aggressively or anything of that sort, unlike some Presidents whom came after him (Bush Sr., Clinton, Obama, etc.). Carter created peace between Israel and Egypt and didn't really change anything else much in regards to the Israel policy of his predecessors. Also, even if Mondale was/acted pro-Israel, it is very surprising that Jews swung 16% leftward in 1984 in comparison to the national average when nearly every other demographic shifted rightward in that election. BTW, was the Iran hostage crisis that important to Jewish voters? Or did many Jews think that a radical Islamic regime is anti-Semitic and Carter must therefore be punished since he did not stand up to this new regime?
I could be wrong, but I've read that American Jewish opinion was substantially more pro-Israel at the time, and the Israel-Egypt accords weren't actually that popular.