The humans were having a rave. The music was old-fashioned techno music as one would hear in the pre-shattering era known as the 1980's and 1990's. The music flashed, many had glow-sticks, the dance floor flashed colors and there were bright, but harmless, laser lights. And a Vorax raiding party, landing on the planet, stumbled into the rave by accident.
Just in case someone's not been to a rave or heard rave music at it's most wild, basically - it's this, but a lot louder with a lot of heavy bass due to the types of speakers they use.
Party planets were thought to be soft targets. Why not? They had lots of resources, lots of financial boons, and lots of wealthy people to ransom for more goods and financial benefits. It should have been an easy raid.
'Should' is not 'is'.
They landed to surround a high cluster of the population, armed, armoured and ready to conquer. They blasted open the doors, and were immediately blasted by what was inside. Weapons-grade sound, irregular flashing lights, nauseating combinations of unnatural colours... and the people within were gyrating around in seemingly impossible ways. It looked like they were suffering from intolerable spasms. To a casual observer, it looked like they were narrowly missing each other in a wild, aimless combat.
But they were also smiling...