It states that Iran is not officially objecting but causing problems via proxies. The news does not say what problems are caused, though.
But the oil smuggling logic makes lot of sense. India also had similar problem of smuggling of petrol and diesel by fishermen. The benefit per litre comes to around Rs 20 and after commission to agents, it still becomes Rs 10 profit. But with hikes in price of petrol in Pakistan, this is unlikely to happen anymore for India at least.
Considering that Iran has serious sanctions on its face, it is highly likely that Iran wants as much revenue as possible by smuggling oil products and will find it difficult to survive without any income source.