This seems like it should be "cream and jam." At least I've never seen a doughnut filled with "oil."
I'm not sure which sufganiyot you've been eating, but the ones I ate are definitely full of oil.
It doesn't literally mean that they are filled with oil (as with jam), but rather have a lot of oil in them, which is absolutely true (but they're so good!).
Not literally filled with oil, of course. Sufganiyot are fried in deep oil, (sort of like potato chips,) therefore they are very oily to touch...
Because of Hannukah's close association with oil (miracle of temple oil lasting for 8 days instead of 1) it is customary to eat oily foods like latkes and sufganiyot, which are both fried in oil.
No, sufganiyot are definitely distinct from doughnuts and are made quite differently. As an Israeli raised and living in the states I could tell them apart on a blind taste test any day. If you really want to, you can refer to them as "Hannukah doughnuts" and it's certainly easier to explain them to Americans as doughnuts, but they are not the same food.