Since when has turbulence caused a plane to turn back unless it was that severe that it caused structural damage?
How were the crew to know the aircraft hadn't suffered structural damage? It's not like there's a big, flashing, 'Structural Damage' light.
They were obviously concerned enough by the severity of the turbulence to suspect something might not be right, so did the safe thing and returned to PER to get it checked out (as reported in the article).
If there's no damage then they still did the right thing by addressing their concerns. Only they can determine their actions because only they were there, unlike second-guessers.