No, the volcano caused the eruption. Who caused the bus explosion? You are fixated on the grammatical parse tree instead of the reality conveyed by the grammar, what happened in the universe and what information is conveyed.
Maybe this is just the programmer in me but it really feels like the difference between an abstract syntax tree and an IR is apposite here. You're evaluating at the wrong level. But also: who's to say the bus didn't decide to blow up all by itself? The bus can be the agent, the same way the volcano is.
If you think that couldn't happen, you never rode in my 2011 Audi A6 that blew up on the Ike, and that I parked in a CPD parking lot, flames jumping out from under the hood, and walked away from like a fucking Batman villain, clicking the key fob just to hear it go "beep-boop-beep" one last time.
There is a link right there in TFA that explains what happened to the bus. The bus was not your Audi. It did not spontaneously combust. The bus was involved in a conflict that was a hot-button issue even back in 2011, and the quoted headline "Bus Blows Up in <CITY>" was blatantly excluding information. Language exists in context.
When the commenter above says "functionally passive", he is getting at something that lies outside of any strict grammatical sense. It is not a matter of ASTs, IRs, or anything of the like. It might be less confusing to phrase this as "spiritually passive". We're using "passive" not in the technical sense but in the normal, colloquial meaning of the word.
Normal people often use the grammatical term "passive voice" to casually mean "this sentence does that 'passive' thing where it omits key info about agency and responsibility". This casual usage makes a lot of sense, because the technical "passive" is our most useful tell for the spiritual "passive". Granted, anyone who takes a moment to think it over can see that there are counterexamples, and that this tell is merely a loose correlation, not an ironclad correspondence. Normal people are okay with this sort of situation.
Pedants are within their rights to be annoyed by this usage (and perhaps genuinely confused, though I doubt that this is common). There is certainly no law against being angry or snide whenever a word has multiple, related meanings. But TFA is just plain wrong when it claims that the passive voice "has nothing to do with lacking energy or initiative, or assuming a receptive and non-directive role." It is entirely related -- by correlation. Correlations are not foolproof logical rules, but people can see them and use them.
Moreover, normal people can see when Orwell or Strunk & White point out a correlation. They can read intelligently to understand what Orwell and Strunk & White really meant, and how it applies to actual headlines and sentences. And finally, they can read Pullum here call Orwell's essay "overblown", and decide for themselves whether Orwell is overstating the dangers of official language, how it can serve to dehumanize and deflect, or whether, more likely, Pullum is overstating this stupid nitpick about what "passive voice" ackshually means.