The article is about the use of ultrasound imaging to study articulation.
This portable technology, which became affordable to linguists around 2000, allows researchers to see the tongue as it moves in real time. It is one of the only medical scanning devices that can keep up with speech; MRIs, for example, are too slow.
Thanks to this emerging technology, [researchers] have documented some of the fastest sounds in human speech: the click consonants present in many rare African languages. Because linguists did not know exactly how the clicks were produced, the sound was placed in a “mixed-bag” category of the International Phonetic Alphabet.
Up to a point, Lord Copper. (OK, if you don't get the reference, go here.)
I wonder what evidence there is that clicks are “some of the fastest sounds in human speech”. Impressionistically, I’d have said that clicks (= sounds produced on a velaric ingressive airstream) are no faster or slower than sounds produced with pulmonic or glottalic airstream mechanisms. I suppose the claim is trivially true, in that the postalveolar (retroflex) click [!], for example, is similar in production to the plosive [ʈ], except that it involves a different airstream mechanism. And plosives are fast(ish). The dental click [|], on the other hand, is typically somewhat affricated, which means it is not so ‘fast’ a ‘sound’. And presumably pulmonic-airstream taps and flaps are the fastest of all.
It is not true that previously linguists “did not know exactly how the clicks were produced”. We can quibble about what knowing something “exactly” might be, and who the unspecified ‘linguists’ are; but phoneticians have been familiar with clicks and their production at least since the 1930s. There is a clear account of click production in, for example, Westermann and Ward’s 1933 Practical Phonetics for Students of African Languages. Their schematized diagrams are pretty good, too.
It was Pike, in his Phonetics (1943), who systematized the classification of airstream mechanisms, describing that of clicks as “velaric ingressive” (or “oral ingressive”).
Nor is it true that clicks are ‘placed in a “mixed-bag” category’ on the IPA Chart. They are in a box clearly labelled Consonants (non-pulmonic), along with the implosives and ejectives that occupy the other columns in the box.
Miller’s research, published in 2009, may well have “organized the clicks based on attributes such as airstream (where the air comes from), place (where the mouth constricts) and manner of articulation”. But in doing this she was merely following a long and established tradition. It is fifty years since I was taught this way of classifying clicks (and all other speech sounds), and I passed it on to my own students throughout my teaching career. I assume all teachers of general phonetics do likewise.
And of course ultrasound imaging in no way enables us to “translate dying languages”, though it might aid us in describing them.