BA ( and Lufty) are dealing with the paying public who can choose whether to fly with them in the future or not.
BA are cancelling flights for a whole week, disrupting hundreds of people's travelling plans. There is also the minor issue that the media will be over this like a rash.
IMO BA ( and it appears Lufty) simply had to say something a bit more than " we've cancelled all flights for a week and we are not telling you why."
Looking at the BA letter upthread it says in part they "constantly review (our) security arrangements.." and then goes on to talk about further assessments.
That looks like suitably crafted lawyer speak which is close to being as vague and non-specific as you can get...