What is true is, that you could give declarer a lot more problems by returning DJ at trick 2. Declarer ruffed the third and played SA, felling her own K, and had 10 tricks. 7 C4 Ux had an awful hand to bid, especially after the rather innocuous 2S overcall. That is I would have bid 3H, not 3S and 4D if given the chance. Since JTx of diamonds fell under AKQ the D9 proved the twelfth trick in NT as well.
T Let's leave the bidding aside, and consider the defense.
Then we will either get two C tricks or a C and a S for down 1. However, S unaccountably cashed CK and the hand was over. This seemingly innocent partscore now cost 3 imps instead of earning 3.