Sure some will say it was turned around because of the CPC's job in highlighting the Liberals attributing something to Harper that he didn't say. But journalists were decrying the Conservatives as having blundered in doing so too.
So without any likely explanation for a sudden drop in people's views of Harper followed by a sudden jump, its more reasonable to believe that their support didn't change significantly and it was just a statistical movement about the true average.
Everyone appreciates that its journalists' job to analyze the latest data and try to present a good story to explain movements in polls during an election. But lets not get carried away by single day movements within the margins of error.