They were called to investigate, so they can ask for ID’s of everyone involved. That is legit.
They did not just request identification out of the blue.
However, see:
http://www.freerepublic.com/focus/f-news/2594740/posts
Sounds like the cops admitted they didn’t have any real probable cause. They can’t just ask for ID without it...
That’s not how it works. John Q. Citizen doesn’t decide. The cops are required to assess the situation when they arrive on scene in response to a complaint call. Often they have to tell the caller/complaining witness that there is no violation and they have to walk away.
Just because someone is upset about something doesn’t mean they have a legitimate complaint that LE can act on.