No, not really, the Democrats simply go with Ron Paul on that list, Obama really should have been included.
If we go to bizzaro world, and only Democrats could vote in the general election, and the only 2 choices were Ron Paul and Mitt Romney. They would pick Ron Paul?
No way!Eh. Paul would certainly take a larger share of the vote in that scneario than in one where only the Republicans vote. Turnout would be lower, obviously.
Paul would win the younger Democrats' vote, obviously, and that's what's going on in the poll here too - Democrats are a clear majority on this site, and Paul is simply the candidate selector result (among those four options) for most of them.