Perfectly normal bidding will sometimes lead to a poor contract, and that is what happened here.
There were two minor suit aces to lose, so success depended on holding the hearts to one loser. There are very few lies of the heart suit that would allow that to happen, but South found a way to do it.
South played dummy’s queen of diamonds at trick one, losing to the ace. East led a deceptive low club. A low heart, instead, might have defeated the contract, but that would have been a dangerous play. The low club was a good effort. There was no deceiving South in the club suit today. He won with his king and continued with the queen of clubs. East won with his ace and now shifted to a low heart — low, 10, ace.
South cashed two rounds of trumps, followed by the king of diamonds and the jack of clubs. He exited with a heart to West’s queen. West had only minor suit cards remaining and had to yield a ruff-sluff. South ruffed in hand while discarding the heart loser from dummy. Making four! South was a bit lucky, but he put up a good fight and he deserved his result. The underdog won!