If the dude was on public and not private property I can't see how they could arrest him. If he was on private property then I can. Weird in either case, though.
Even if he was on a public sidewalk, you have to keep moving, else you can be arrested for loitering or one of a hundred other offenses depending on local regulations (impeding foot traffic, etc). This is why demonstrators and strikers are walking, rather than bringing lawn chairs and sitting.
Yeah, "freedom of religion" and "freedom of speech" don't mean "freedom to stand wherever you want and do whatever you want at any time". I hope this guy wasn't teaching civics.