Why wouldn't he include the credits? And why are the credits not important to someone who has worked with most of the people that would be named there intimately?
A typical TV show runs for 30-60 minutes, right? But ask the cast/crew how long they are and they might say 22-44 minutes, because that's how long the story is (credits length is negligible, lasting maybe 30 seconds).
So, when asked how long his movie is, the director might respond with the time from when the story starts to when the story ends.
And I never said it wasn't important to him. But the director doesn't sit down and write down each credit. End credits are, undoubtedly, the very last thing produced though and, unless there is sort sort of gimmick running through them, aren't part of the story. I suspect all the director does is receive the credits, make sure they look the way they should, and attach them to the end of the film.
Aren't directors obligated to include credits whenever they mention runtime?
By whom?
Now, if there is a scene after the credits, obviously Snyder would, of course, include them in his running time. But otherwise, why would he have to consider it part of the time in answer to the question? They asked him how long the movie was and he answered.
Look, I'm just giving possibilities. This is speculation. Maybe he did give the time with credits, but maybe he didn't if the official running time is closer to 2:30.