I think that you haven't given us enough background context to say with any degree of confidence what was going through, or not going through, the writer's mind. It could well be, for example, that the writer simply forgot to include the percentage symbol, either at the time of writing the sentence or when reading the text back, in which case I'd call that an editing error, or a typo, as was mentioned in post #2.
It isn't easy to imagine a writer making no conceptual distinction between the number 22 and the percentage 22%, but if the context were, say, a response to an IELTS writing task where the candidate must describe data expressed on a graph, it could be quite possible to be confused between numbers and percentages.