In all reality, there is no way to keep people from talking to each other in pretty much any way they want and the boundaries between what is officially "legal" and "illegal" here are so uncertain, that whatever one hundred volume treatise an army of crooks may write on the subject, it will just confuse everything and clarify nothing.
As to the formal question, AFAIK, the freedom of speech act won't help you much if you are doing something utterly ridiculous (like posting the questions you were explicitly asked not to spread on billboards, online or otherwise), and any legal dispute will be resolved based on the circumstances more than on the action itself, if you decide to bring it to that stage. In general, universities can and do enforce written academic policies against obvious violations and within reasonable limits, but, like it is with copyright, speed limits, and other things, it is understood that an attempt to stick to the letter of the law no matter what will make more harm than good, so you can get away with "minor infringements" more often than not.
As a side note, a professor officially complaining about students complaining about her makes me just laugh: if we had all followed the pattern, the courts would have to work day and night for the next few decades. The article carefully avoids telling what exactly the posts were (and, knowing what our students write in the evaluations, I am ready to believe that some of them might be offensive enough to merit a good slap on the face) but going the official way about such stuff just doesn't seem to lead anywhere. If you are dealing with legitimate and civilized criticism, you'll just have to swallow it, though you may prefer to stay at your own opinion, and if you are dealing with morons, you will just waste your time on them and gain next to nothing even if you win. You'd better leave the judgement about the validity of student complaints about you to your colleagues and other students: most of them aren't blind or stupid and know who is worth what.