What I don't see mentioned in the article is that most birds seem to live on a much faster timescale than humans. If you record and slow the song down, you can hear far more nuance in it.

BTW the Merlin app mentioned in the article is fantastic. Having it for birdwatching is like having a GPS map in the city, especially when paired with a good directional microphone. It only tries to identify a bird itself, though, without attempting to decode the type of the song.