The part about Zork doesn't make sense to me. As I understand it text based adventure games are actually quite lenient with the input you can give, multiple options for the same action. Additionally certain keywords are "industry standard" in the same way that you walk using "wasd" in FPS games, so much that it became the title of the documentary "get lamp". Due to the players perceived knowledge of similar mechanics in other games you can even ague that providing these familiar commands is part of the game design.
It seems to me that the author never played a text based adventure game and is jut echoing whatever he heard. Projects like 1964's ELIZA prove that text based interfaces have been able to feel natural for a long time.
Text has a high information density, but natural language is a notoriously bad interface for certain things. Like giving commands, therefore we invented command lines with different syntax and programming languages for instructing computers what to do.