I'd speculate that the simplest root cause might be an system overpressure. Any hookup to a valve that couldn't contain a pressure of some level could be susceptible to leaking gas onto an ignition source which could then start a fire.
A gas explosion (claimed to be among the biggest non-nuclear explosions) was caused by the CIA hacking a soviet pipeline: https://www.telegraph.co.uk/news/worldnews/northamerica/usa/...
No idea what caused today's explosion, but the USA is clearly not without enemies and vulnerabilities in its own infrastructure.
Yet its also too destructive and attention seeking to be a plausible threat or sending a message; if outsiders messed with the SCADA to do this, fifteen minutes later all the passwords would be changed and sites physically locked down, such that a threat to do something more destructive next time (or else..) such as flicking the gas supply off for a couple minutes would be a non-starter. You have to look at it militarily like a stealth attack; giving away your position is not a wise first move if your whole strategy is stealth. You get one shot and this would be an intentional miss, so ...
This would also imply its not an inside job; an insider would know that in my state (admittedly not MA, thankfully) an interruption in pressure requires an attempt at physical access by a rep with a leak sensor to verify pilot light and pilot light safety interlock for EVERY point of use and/or door tag notification warnings. Its happened to me a couple of times for some street work replacing pipes and replacement of my old meter. Its kind of an expensive labor job, a wealth transfer from the company to the union. The fact this didn't happen kind of exonerates the union.
So rule out outsiders and insiders. A nutjob would probably drive a truck into an above ground facility, or frankly, just drive into people, so its probably not a nut. Not many options left. Space aliens did it accidentally? Maybe they closed down that solar observatory in NM because the space aliens are coming to mess with our delicious natgas.