Two possibilities:
1.) Made using plasma scalar-wave inferometers from a ship in orbit around Earth, or in the Sol system, as a real answer to various beamed radio messages from Earth (see SETI, etc). A real answer.
2.) Made using plasma scalar-wave infereometers by a government-backed or Breakaway Civilization here on Earth as a disinformation tactic to continue the UFO disinformation policy. A spoof, in other words.
To get an idea behind the technology, look up LTC Thomas Bearden (ret) and his scalar-wave inferometer technologies (http://www.cheniere.org/index.html). These are the "fiery globes" often seen at night or in the early morning creating crop circles in just a few minutes. The plasma globe can be directed as easily as the ink-head on a fax machine or laserjet printer, and with similar speeds.
Thanks for your input. I'm somewhat familiar with these theories. I can assure you however that there could be a multitude of other potential possibilities as well. In the end, we don't really know, do we? Hopefully, things such as this will get cleared up in the near future? We'll see.