Very possible. But then the Iranians are notorious liars so it's possible that it was just a lucky shot (owing to the fact that mortars are very difficult to aim with accuracy). I note that the article headline claims that this is some sort of pattern but doesn't site any other incidents.
Since ISIS is Sunni (Salafist) and Iran is a Shiite regime (which has made some recent partnerships with the Shiite Alawite Assad faction) they are never going to get along very well and have a long history of BS related to their wars.