I think the man's only crime here really is the fact that his tune is slightly monotone and repetitive.

He says he used to sing, but switched to whistling.

Perhaps that's a good thing but apparently not everyone in Portland has a sense of humor and they've complained leading to a court order that basically allows him to keep whistling, but he has to stay on the move so as not to become too irritating in one spot near downtown Portland merchants.

Personally, I think the guy could be exhibiting much more troubling behavior than whistling a happy tune.