The line art shows the outline of a Boeing 787-8 airliner; you can watch the image being drawn in real time in the video shared by Boeing (above).
The flight was conducted for testing of the 787's Rolls-Royce engines.
Boeing spent Wednesday evening drawing an airplane on the sky.
The aircraft headed first towards Marquette in MI, later hitting regions in South Dakota, Wyoming, Colorado, Texas and Alabama, among others. The nose of the plane traced by the route pointed toward the plane's home airfield in the Seattle area.
It appears clear that the flight was not a result of the pilot getting catastrophically confused, but part of an elaborate PR stunt - which wouldn't be the first time Boeing has done so. It covered a total of 9,896 miles. Just in case you're curious, the longest commercial route today is the flight that links Doha, Qatar to Auckland, New Zealand. Imagine being on a plane for so long!