This article makes some big logic jumps... The fact that they used Apple loops doesn't actually mean they used iMovie. The loops Apple includes with iLife are

This article makes some big logic jumps... The fact that they used Apple loops doesn't actually mean they used iMovie. The loops Apple includes with iLife are usable in Garageband and iMovie, yes. However, they also show up as loops in Soundtrack Pro, Apple's pro application. It seems much more likely (being someone in the media field) that they used Final Cut Studio and processed the audio with Soundtrack.