Don't you realize that the aliens obviously have the tech to disguise their ships as signal flares???
Not to mention their soldiers are disguised as discarded rubbish? We're surrounded!!!
Having actually been a test engineer in the past though, they may have been using camera equipment to track the plane (or just the flares) visually, while it dropped the flares as it was being filmed? Maybe? I dunno, I might be crazy. I know when things with any kind of technical sophistication are involved, the tests created are completely up to the imaginations of the people who are working with/on it. There's almost always something worth seeing from the test results that wasn't expected, or needs to be verified through multiple kinds of observation, so the more you add to the test to observe, the better.
One thing I would use the radar/flare test for is to see if long range visible light systems can track in synch with radars when it comes to range finding and doppler effects from objects in motion, or to calibrate a visible-light based system (and/or infrared) with the radar system, since the flares literally cover at least those three spectrum.
Why would one do this in public? It's (probably) not involving secret tech, and the land based part of the test probably wanted to show off to family or just thought it would be cooler :) I'd show up to watch if I had nothing better to do. And everyone loves pyrotechnics ;P mmmm, fire.
Of course it could be the government getting us used to weird things happening so that when the true alien overlords do finally show up soon, by the time we realize it isn't a hoax we'll be easy pickings. Of course. Or it could be....
Mine's the one that says, "My tinfoil hat is my other pants"