I am no expert here, but yes there is a difference between the two . They are both from the Oleaster Family and both are listed as invasive. Russian Olive's scientific name is Elaeagnus angustifolia and the Autumn Olive's is Elaeagnus umbellata. Here in New England, at least, it is the Autumn Olive that is our invasive nemesis.
Perhaps the best way to tell them apart is that Russian Olive has stiff thorns, and the silvery scales that adorn only the bottom side of an Autumn Olive leaf, are on both sides of a Russian Olive leaf. And this time of year, one would see on the Russian Olive a more yellow to orange colored fruit, instead of the bright red of the Autumn Olive.
While I am no fan of this invasive, I must say that I have grown to love the fragrance of their flowers in the air in late May. The first whiff just stops me in my tracks. And their high density of the antioxident, lycopene, has SOME looking to make a cash crop out of the pest. Check this out.