A bomb in the cargo hold could also cause this, but terrorists usually try to make it obvious that an incident is terrorism. An incident that gets passed off as an accident doesn't suit their goals.
Because of that, terrorism seems very unlikely in this case. It should be investigated, and with what little they know it is a possible explanation, but there is little reason to believe it is a likely explanation.
One of the commentators on TV, shortly after the Airbus went down, said that the terrorists who blew up the Pan Am plane expected it to do so a little later when it was over water, not when it was over Lockerbie, and if that had happened it might have been hard to demonstrate that it was a terrorist act from the evidence that would have been available.