...hitting the runner in the back when he's out of the baseline may sound good in theory and it might get the runner called out but you just never know for sure, especially today when the HP ump was bad all day in every facet of his duties.
...but in Betances defense, on a band bang play like that you're simple trying to get the ball to the 1Bman as quick as you can, and I doubt that the brain processes the play and the rules of the game that quickly and realizes the runner is out of the base line and a little voice in your head goes off and says "Oh, he's out of the baseline, hit him in the back and maybe they'll call him out".
...but it's still hard to believe that both the HP ump and the 1B ump could not see that the runner was clearly running on the grass instead of the chalked baseline box the whole way...as Charles Barkley would say, "Turrible, just turrible".