How do you know it doesn't always do both, depending on how you enter the singularity ?
I'd imagine it still would, just in a million pieces. It's possible that the debris from Vulcan traveled through time as well.
But I think the point was that the red matter black holes were so magical and beyond what we actually know of as black holes, that they really only did what they needed to (stop "supernovas", travel in time, implode planets, attack enemy ships, etc.) They weren't given that much thought.