The graph shown is for the popular vote, not the winner of the electoral college. Gore won the popular vote in 2000 and this was accurately predicted by the Iowa Electronic Market.
Are you sure about that? They have a "U.S. Vote Share" and a "Winner Takes All." I never did know if IEM was for an actual win, or for a simple popular vote. Seems like kind of a silly market if just vote share. After all, shouldn't the futures be traded on the actual outcome (Dem or Rep)? That is the point of the Congressional futures.
I do recall the final pricing for 2000 having the Dems win, so it did look like a popular vote thing. I didn't know when they cut off trading either and with the results delayed, the whole thing seemed simply screwed up to me.