Really? The world is full of random bits of information that people may or may not need to know. He was not appearing as CAS (yet!), there was absolutely no need for him to know this specific little nugget. This was down to an mp deciding to be difficult because they can and he sensibly took the option of saying 'i dont know but i'll get back to you'
Senior officers are not supermen blessed with massive memory anymore than the rest of us. I'd rather he spent his time doing his actual job, not prepping endlessly for whatever unlikely snippet of information an mp wants to ferret for i an environment where the mp's can, and do, go for the kill on utterly pointless matters.