Underruff

Yes he had. Instead of playing ♣K from dummy, he could have come to the hand in ♦ A and play the ♣ from hand. If LHO takes the A and play a ♠, you can ruff another ♥ in dummy and discard 3 red loser on 3 ♣s, if someone ruffs from 3 card ♠,  you are home. Taking ♣ A might look wrong for this deal, but it could be correct for plenty of other lay outs, for an example, if West gives declarer a hand like  Qxxxxx Qxxx AK x, which is consistent with the South bidding , taking the ♣ A and playing ♠ would ensure 3 down, while he allows to make the contract by not taking that ( declarer will score 7♠ , 1♣ and 2♦ ) .

Anyway, if West ducks, you face a difficult choice. At table, you would know that your LHO has the A but that does not solve your problem. You need to guess the position of ♣ 10 and/or the ♣ distribution. playing K and Q of ♣ , playing 9,  playing K and then go for a cross ruff line all can be successful based on ♣ distribution and ♣ 10 position. If LHO has A10xx, you should play 9 (you can also make by cross ruffing if RHO has 3 ♠ or LHO has KQ9 of ♠)  , if LHO has Axxx, you should continue with top honors (you can also make by cross ruffing if RHO has 3 ♠ or LHO has KQ9 of ♠) and if LHO has Axx you should cross ruff ( if LHO is dealt with A10x, you will always be successful but he should never duck from that holding).

Difficult problem and it is generally helpful to put yourself in LHO’s shoes in these situations. Obviously it is also very important how you rate your LHO.My feeling is, every player thinks up to his level and when he tries to find out what declarer can do, he tries to judge by his level of thinking. For an average player, it might be tough to visualize that declarer might put the 9 as well, so he might not duck from Axxx, as t it would not make any difference for him. If we go by  the assumption stated above, your LHO can have two distributions : Axx and A10xx. The theory of vacant places indicates that chance of 4♣ s with LHO is higher and you are going to put the 9,