Well, both happened. Pittsburgh's home run output increased from 140 to 153 this year, but the Bucs dropped from 10th to 12th-most in the NL. The Royals (147), Giants (130), Marlins (128) and Braves (122) were the only Major League clubs to hit fewer homers than the Bucs.
The Pirates were an above-average pitching staff in terms of preventing homers this year, but they were not immune to the trend either.