You can't be certain that Pakistan is ruled out from the conspiracy. Hence why I said they are a suspect and gave my reasons and evidence. No matter how organised Iran border force is, when you have a state backer allowing terrorists, whichever way imaginable, to launch attacks from their side of the border, you will end up with incidents like this. Look at western backed Ukrainians inflicting pain on Russian territory as another example.
You can rule out Pakistani involvement for reasons only you know, and I suspect, but I certainly won't rule them out.