This headline feels slightly misleading to me. As far as I can tell, this research shows that sperm whale clicks have spectral properties <i>which are analogous in some ways to human vowels</i>. In particular, they exhibit formants (essentially, amplified frequency bands), and analysing them reveals that these whales produce two different kinds of clicks. While fascinating in their own right, I feel it isn’t entirely fair to call these ‘vowels and diphthongs’ without qualification: these seem to admit a lot less variation than do human vowels.