Classrooms teach about reality (among other things) and there are many things in reality that don't involve obedience to the law, as it exists at a particular time and place.
See also: https://en.wikipedia.org/wiki/The_purpose_of_a_system_is_wha...
Follow-up question: Does an enclosed stall count as "public space"?
Look at the photos in the article, they weren't enclosed stalls. Its elegant in a way, just a couple feet of opaque material that wraps the beltline of a central aiming point. Basically as good as going on a tree but without people getting uptight.
When it's one person, true, but when it's a population, the politics historically changes and the law accedes to pressure to stop enforcing that determination.