I'm not personally sure if 'prehistoric' is the right terminology to use (I prefer pre-European or pre-contact in this context), but he is right that much of pre-contact North America didn't have any real sort of writing.

The closest things the Midwest had to writing were the semi-standardized pictographs of the Ojibwe and the Dakota winter counts. The former used pictographs as mnemonics for songs, genealogies, magic, and sometimes personal messages. Out on the Plains, winter counts marked the most notable event of the year with a symbol.

Though they do record information, and in some cases there were writing-like elements, neither of them are true writing. They don't convey a language, there's no real set of rules and the meaning of the pictures are mostly dependent on what the artist wanted them to mean, or sometimes even reader. In the case of Ojibwe song scrolls, the same set of mnemonic glyphs can be used as a visual aid to an entirely different song.

The only examples of true writing we know of in the entire Americas is Maya writing in the Yucatan, which is fully capable of visually emulating Maya language. Proto-writing existed elsewhere in Mesoamerica and the Aztecs had a written glyphs for calendric and accounting purposes, but the closest they came to the spoken word were glyphs for place names constructed using the rebus principle, which used existing glyphs as phonetic elements combining them into a word that almost sounds like the place in question.

Today, some Native American languages do have their own writing systems. Most of these were crafted by missionaries to teach natives to read Biblical passages. Cherokee script is an exception, being developed by Sequoyah after watching writing being used among whites.