It may take a decade or more to reveal the truth about this incident. Right now there are a number of plausible suspicions. The author reports on some of them.
Three years ago, ABC News, quoting US and Pakistani intelligence sources, reported that Jundallah, which was created in 2002 and carried out its first attacks three years later, had been "secretly encouraged and advised by" US officials since 2005.The same tactic was applied to Iraq. See this, this, and this.