That's not what knowingly means in this context. Knowingly refers to the level of intent required to pursue charges, not whether they knew there was a law against it.
In this case it requires the government to show that the person intended to leave a review and/or testimonials that misrepresent that they are by someone who does not exist.
It prevented reviews and testimonials that misrepresent that they are by someone who does not exist. Fairly easy to prove. If they catch an individual posting a review while posing as anyone but themselves, It's a done deal.