I can totally understand why the on field umpire gave this one out, but DRS was correct. There has been more bounce in the wicket today which will have affected the ball tracking predictor on Hawkeye. (remember, a prediction tool is all that it is.) Earlier in the match, conversely this might have been predicted as out on DRS.
Looked plumb from the front before the side-on view showed he got a proper stretch in. Although, I don't think it was bouncing that far over as DRS suggested.
Right decision in the end but I can't blame the umpire on that one.