I think more study is needed if this was the overly simplistic conclusion they got.

Alphanumeric alphabets are series' of symbols that work in sequential combinations to form words, where what is described as *symbolically written languages* use each symbol as a word which is then used in sequence with others to form sentences.

Or is my understanding overly simplistic?

My reference is Scott McCloud's 'Understanding Comics' and his telling of the history of drawing & how drawings became writing.