On the other hand it looks almost too normal. Odd.
It could indicate bias on the part of the researchers. I haven’t read their methodology, but in my amateur study of languages, some languages have some interesting tricks for communication that don’t translate to English well or efficiently. If English was used as the baseline, then the study ma not incorporate some of the neat things other languages can do as points to measure.
Mandarin has a word particle to communicate “completed action”. This is used instead of conjugating verbs for tenses. Example: in English you might say:
“I went to the shop” 5 syllables
In Mandarin the literal translation back to English would be:
“I go to the shop [completed action]” 5 syllables
For the two measures listed of essentially Information Density and Speech Velocity, this benefit wouldn’t show up, but if you’re measure for something like Encoding and Decoding Burden (I’m making up these terms), then Mandarin could rank higher.
Cantonese and Vietnamese make sense, as they’re are both tonal languages (along with Mandarin, Thai, Punjabi, and Cherokee apparently). English wastes tones on communicating stress or question vs statement.