"Ambiguous" does indeed refer to a word or phrase that could have more than one meaning. Usually language is "ambiguous" as it relates to the context and words surrounding it. But it is not wrong to use it in this case, either.
However, there is more.
In this book, you'll find that not only are there two ways of looking at concepts like "Big Brother", but also that a powerful group of people who control the conversation are trying to give the impression that one way ways of seeing a concept is true, and the other is not. They have chosen the exact words, setting, or impression carefully to support just one interpretation.
They are therefore engaging in "propaganda".