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Firstly, wow, that is absolutely insane.

I'm wondering about this part though:

> The source of the finger-swiping sounds can be popular apps like Discord, Skype, WeChat, FaceTime, etc. Any chatty app where users carelessly perform swiping actions on the screen while the device mic is live.

Is there really enough information left for this method after the sound has been lossily compressed by any of those apps?

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that was my first thought too, this kind of reminds me of the 'figure out which key was pressed by listening to keystrokes' trick.

That attack is more about timing than about sound. There is some information available from the sound of a keystroke, with a very good microphone under ideal conditions each key could be identified uniquely, but that's not the main vector. Some sequences are easier to type than others by their very nature, and individual typists have idiosyncratic variance in how easily/fast/accurate they are at a given sequence. That's the main trick used to derive what's typed from a recording of it happening, and compression doesn't reduce that information, so long as the keypresses are audible.

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