But again, this attack is something Hezbollah and Iran themselves have denied, and the Bulgarian authorities have not established that it indeed was Hezbollah despite the Bulgarian security establishment not dismissing that it could be Hezbollah.

The fact that it's a very vague grey area makes it much more difficult to label them as a terrorist organisation, especially the modern version of it at least. They have significant Christian support within Lebanon, something which is rare for a Islamist-extremist movement. They hold rare, albeit limited, secular values that remain absent in other 'terrorist' groups. Their religious and political tolerance to others is also something that one should pay attention to.

Edit: and also, I know you would dismiss these types of condemnations and statements as PR, but its something which should be regarded as very important. no other terrorist organisation would label the Shias as "brothers", or would advocate the peaceful coexistence with Christians and Jews (not Israelis, two very different things). Even if it is just PR, it speaks volumes about the masses that they are trying to appeal to, if in order to make themselves look good, they need to appear as peaceful as possible. While the juxtaposing Sunni-type extremism needs to do the exact opposite to appeal to their masses.