I think you're hitting on the fact that there are multiple variables that contribute to "quickness." Having digested a lot of background material is definitely part of it and ties to the higher up posts about e.g. Churchill. Also a way intelligence can correspond to it, in the sense that more intelligent people have often digested more topics. But there also seem to be people who are less distractable, more tuned in to what is going on, and more able to tie current happenings to their body of knowledge and make a joke or whatever.