Wonder if Pakistani jihadi trainers were involved in the 21 Iraqi terrorists accidentally going BOOOOM?

I very much suspect it was so. There's a deluge of Pakistan Govt-Saudi backed Pakistanis training Saudi-backed jihadis and it's more than possible that some of them are already in Iraq.  

Taimur Khan  writing at TheNationalAE:
Saudi Arabia and Pakistan forge stronger strategic alliance.  
Saudi Arabia and Pakistan are expected to sign an agreement on security and defence cooperation when the kingdom’s crown prince visits Islamabad this weekend.....

.....During his three-day trip, Gen Sharif met King Abdullah and military officials to discuss plans for a “new era in strategic partnership”, according to a Pakistan army spokesman.
Analysts say both countries are looking to deepen their strategic military ties as the US begins to shifts its resources......

.....While Pakistan is helping Saudi Arabia train Syrian rebels, according to Saudi sources first quoted in a report by the Carnegie Middle East Centre in Beirut, Riyadh’s most pressing security priority aside from Syria is Iran, especially as the US negotiates a deal over Tehran’s nuclear programme........

....“It appears that the KSA was unable to expand the training programme run in Jordan with US cooperation to the much larger numbers it seeks to train, and so the Pakistani army is a good alternative because it is professional and capable, as well as having a long-standing relationship with KSA,” said Yezid Sayigh, a senior scholar at the Carnegie Middle East Center in Beirut.....

From DailyMailUK:
 ...Gang of 21 of Iraqi terrorists  accidentally blow themselves up - while making promotional video about the joys of suicide bombing
The explosion also resulted in two dozen arrests, Iraqi officials said
Police officer said militants were attending lesson on making car bombs
It is believed the explosion occurred when a glitch set off a device........