The blue line is the estimated support for the President at each point in time. The gray dots are the individual polls which vary randomly around the estimated support. Each poll will differ from the common trend due to sampling variation, question wording or order among other idiosyncratic factors. The estimated support is based on a local regression which can flexibly fit the trend in the polls.
Each of the smaller charts below plots a red trend line for the polls from the individual pollster. Keep in mind that the size of the don't know category is a big source of "house effect" variation among pollsters. Those that typically report a higher don't know percentage will also typically report a slightly lower approval rating.
