If you are covering the event, then yes it is. Perhaps the media in question didn't encounter them, but if they did and chose not to cover it, then they would be actively not covering a new worthy presence at the event. Why would one not cover Communists at the May Day gathering if you are going to cover the May Day gathering? That's a preposterous notion to me.
It would've been nice if he had shown the flags in the video. Otherwise, not quite sure of the point.