Agreed - this has been the MO for various terrorist groups in the past. If your aim is to cause disruption (via evacuation) and economic damage above casualties (and this is the aim of some terrorist groups), then this is what is done.

Assuming it's like the old IRA days in the UK, it's also probably not a simple case of phoning up DUS General Enquiries and saying "oh, by the way, there's a bomb in Terminal B". Where terrorist groups are known, there can be a system of code words used to determine the 'genuine' nature of a call.

There have, however, been situations where this has been used to the effect of killing/injuring more people, where a threat has been given, with the intent of getting people evacuated to a specific place, where the real bomb is then detonated.

But I'm no security expert, so I don't know how this kind of threat would be taken these days, nor how the decision on how to act on it would be taken.