In numerical computation, "exact" is a term of art that means providing accurate bounds, that are not affected by random numerical errors. So an "exact" computation of Pi is one that, e.g. might just ask for a minimum precision as input, then provides an interval around Pi that's at least that small and accurately bounds Pi. If the AI answered "it can't be done" that's not really the best outcome, though it's understandable because that use of "exact" is quite niche.