Im not a psychiatrist, and have no experience with Schizophrenics.. Im guessing you do, since you believe you see the signs.
I can sorta understand the decision after the fact not to report it, but, think about it. What if someone else nearby had the same thing happen earlier, and decided it wasn't worth it either?
I agree it doesn't rise to the level of calling 911, but if it happened to me, I'd file a report, with the desk sergeant, which shouldn't take long at all.. possibly less time than spent debating it on this thread. That way, if it is the beginning of a trend, it might help out a fellow citizen avoid similar or worse situation.
Mike