I would tend to believe this one because the same people were polled twice, once before, once after the speech.
The President did a great job of communicating the issues and his plans in a clear, concise, way...IMHO, that is the reason for the positive upward motion in the poll.
Apparently. Looks like it was an effective speech. It's surprising to me though--because my gut reaction as I was watching it was that it was--stylistically- just a good speech-not one of his great ones.