There was no open base, so walking Howard puts a man on 3rd with only 1 out. Much easier to score from 3rd in that situation than from 2nd. Don't forget that after the pitcher, you would have to pitch to Jimmy Rollins again.
Plus HOward is terrible against lefties, he hit less than .200 last year against them. So do you pitch to Howard with man on 2nd, then the pitcher, or to the pitcher and then Rollins, with man on 3rd in both cases?
The right decision was made, the ball just went in the hole vacated by Johnson holding the runner.