Let me explain something. Here in OK we have a lot more registered Dems, BUT they vote Republican. Most of them will not switch until their parents die but vote straight Republican in the federal elections. That means here in OK if you use the number of registered Dems, it will tilt any poll toward the Dems. This is pretty much the same across the board in the south.
He's talking about the trend from one poll to the next. If there's too many Dems in all the polls it wouldn't explain the trend toward Webb from Allen. Very simple.