Text and more broadly natural language is actually a stunningly low-bandwidth form of communication. The reason it works so well despite being low-bandwidth is that we humans share an incredible amount of shared experience and common knowledge, and so the limited amount of information in text can refer to a much wider set of knowledge and assumptions and our brains are able to make inferences and use context in a remarkable way to fill in the blanks.
To take an analogy, think of writing text as analogous to compressing data using a Huffman code. Our ideas correspond to the initial uncompressed data, natural language text corresponds to compressions of those source data, while our brains correspond to the Huffman tree that tells you how to decompress. With our brains/context we can recover the initial ideas, just like with the Huffman tree we can recover the uncompressed data. Without the Huffman tree, the compressed data are gibberish.
On the one hand this means that text is really powerful as the author says; we can store an incredible amount of information in a small amount space, and can reconstruct the source idea the text represents efficiently (if with some amount of ambiguity and error).
On the other hand text is very far from universal. Anyone who sees the Twitter logo sees the exact same thing (interpreting it as a bird, of course, requires the prior knowledge of what a bird is and looks like). However, anyone who sees a piece of text not only needs to understand the language it's written in, but also all of the ideas that it refers to. That's why we still have many examples of languages and texts that are undecipherable: we've lost the context they were originally written in. Even Egyptian hieroglyphics were undecipherable until the 1800s when people used the Rosetta stone to provide context to decipher it.
Text has further issues as well, chief among them its ambiguity. Not only is it easy to under-specify things in text, but it's also possible for the same piece of text to mean different things at different times and places.
As a culture these issues may be strengths; poetry and literature derive strength from this openness to interpretation, and many would argue so does law where statutes written centuries ago can be adapted to our time. But from a purely data storage and transmission perspective, these are clear weaknesses.