I think @Filmstudy’s point is that he went into the slide far away from the bag and his momentum had significantly slowed by the time he reached the bag. I think he’s probably correct, that was my takeaway from the replay.
IMO it was a perfect storm. Singleton is a big guy, doesn’t seem to move well. IIRC the pitcher was late getting over. Cowser was fast enough to make it close, hustles and makes a great play.