Am I wrong for calling 911 when I see a man walking around in public with a rifle?

This blew up into an argument between me and a friend. We were driving back to work from lunch just now and saw a man on the street pointing a rifle at passing cars.

My friend strongly tried to dissuade me from calling 911, saying it's best to not get involved and if you report something and it results in death, "the man" will try to hang it on you because you're now involved.

I insisted on calling 911 so police could figure out what was going on and possibly prevent a tragedy from occurring.

Am I wrong on this?

This was in Denver a few minutes ago.

Update: I did end up calling 911, but asked to remain anonymous.

Also, Open Carry has been illegal in Denver since 1973. You can only conceal carry with a permit or nothing.