I think they meant syllables specifically, not syllabic symbols. Meanings syllabic symbols might get confused for an alphabet if the language has a sufficiently small set of syllables. See https://linguistics.stackexchange.com/a/36909
So, in terms of "possible sound combinations" I think Japanese would likely be on the lower side given that the number of sounds are also pretty low. Alright, thank you for that reply; the point in the original post I replied to makes more sense to me now.