Yelling FIRE in a crowded theater. For decades, the courts in this country, including the U.S. Supreme Court, have ruled that free speech is not necessarily free. In the more recent rulings throughout the U.S. District Courts, justices have acknowledged the importance of free speech and have, for the most part, upheld that basic Constitutional right. The take-away is that it has been repeatedly said that free speech is subject to "reasonable time, place, and manner" restrictions. This is the issue with Furry Potato. The question becomes "was the time (school in sesssion), place (outside an active school with children present) and manner (physical appearance causing alarm) REASONABLE? In the context of things, and considering the totality of the circumstances, I would submit that this situation was not befitting the concept of a "reasonable time, place, and manner".
All auditors need to realize that, despite it not being illegal, their activity, to most, does appear to be somewhat suspicious. One has to take that into account and be aware that reactions can, and often will, be ratcheted up a bit. Is reaction to a "suspicious person" taken too far? Yes, quite often it is, and it is used by authorities to both force cessation of the activity and to punish it. With that potential outcome in mind, it would behoove auditors to ease off under those circumstances, and achieve change through other avenues and approaches (i.e., information and training).
As the article says, just because you're on a public sidewalk, it doesn't mean you are legally allowed to be there. That being said, just because you're not required to identify yourself, doesn't mean you shouldn't to diffuse a situation and dash those "suspicions", potentially avoiding an unnecessary arrest (or worse).