There is a difference between threatening somebody and saying things that could possibly be threatening.
If he had gotten in somebody's face and said he was going to cause them harm, that is a threat and in that case if somebody did do something to him, then that's justified since if somebody does that, you would have a very reasonable fear of bodily harm.
It doesn't sound like he did that. He definitely was saying things that might make you feel uncomfortable, and maybe were unnerving, but he didn't directly threaten anyone. He was unarmed, didn't brandish or intimate he had a weapon, so providing that he was intending to hurt somebody is kind of difficult to do. He obviously had mental health issues, but he wasn't doing anything besides loudly shouting things that might make people feel uncomfortable.