This is the 'collapsing' that he talks about. If one of the complex solutions had a magnitude of 1 and an angle of 395 degrees, e.g., it would be equal to a number with a magnitude of 1 and an angle of 35 degrees.
Thanks (and thanks to the other replies !). So a complex number has a single representation when using real and imaginary parts, but an infinity of representations if you use angle and magnitude (just add or subtract 2π radians). I guess that should have been clear from the article, I just needed to sleep on it.