The article claims less information is encoded in each syllable, not more (as would be expected if more syllables were available).
The Japanese syllabaric alphabets (hiragana and katakana) are larger than the roman alphabet, but the smaller alphabet doesn't mean that Japanese has more syllables than English. English syllables are written using multiple roman letters, and there are far more combinations possible than in hiragana or katakana (hiragana and katakana do allow small letters written between characters to modify the syllables represented, but even taking this into account, there are far more syllables possible when writing English).
On top of this, written hiragana or katakana maps unambiguously to the spoken language, but with English, there is more than one possible pronunciation for many character sequences, and the speaker often needs to know the word and sometimes even how it fits into the sentence to know which of several possible syllables to pronounce.
