If the wrong person was accused, did they say something? From where I was sitting they appeared to leave without any fuss once identified.
And it's well known flares are illegal at the football. Not only is it dangerous, but it brings negative attention to the supporters, the club and the sport in general - we deal with enough people who are "anti-soccer" as it is.
People are well within their right to point out supporters who can cause potential harm to others around them. It certainly isn't "dobbing".