It could be true that a throw that didn't bounce would have resulted in an out. The ball was definitely there in time - the umpire was looking to see if the ball was in the mitt before making the call - but obviously there would have been more time with a better throw. But in this case, short of the batter/runner taking 2nd or the runner who was on second also scoring, I don't think there is a scenario that I would call an error on either 2B or C regardless of where the throw ended up. But, as I have admitted above, I may be biased toward the 2B. Without the diving stop, two runs score on the ball up the middle, and no time to stand up to throw. I would hope given the same scenario, he would make the throw again, whether he officially gets the E or not.