From reading other articles, I think it was because they asked to use the bathroom and they responded that it was for paying customers only (which is fair on Starbucks case), but that still doesn't explain nor justify the manager asking the police to remove the 2 guys. I really hope there is more to the story or this might actually be a case of discrimination.
It seems the manager allowed other non paying customers to use the bathroom and sit there though, so it still could be discrimination