I don't believe the article says that the track you're on doesn't drop out, I think you must have misread something. Remember that the bolded part you quoted is referring to the tracks that you're not currently playing: "What's more, the tracks that you're not currently working on play just fine without your direct input. " That line is referring to the different game design used in Blitz compared to previous lane switching titles. In previous titles, you're required to repeatedly switch instruments to "capture" each instrument track periodically to stay alive and keep a multiplier, whereas you don't have to do that in Blitz. I know this explanation may be confusing, but it makes much more sense if you've played (or watched gameplay videos of) previous games like Unplugged or Amplitude.
I think the writer could have phrased it better, but what he's written is not wrong (as long as the reader understands the gameplay mechanic from past games that he's referring to).