The first thing I want to point out is the Maker's lead is wrong. When one calls with L-A-9 they cannot lead the 9. Leading the 9 creates the possibility of the enemy taking the first trick with a low trump with the Right still being in enemy hands. That's a nightmare scenario that leads to a lot of euchres. The easiest way to avoid that problem is always lead the Left or Ace from this configuration. Always make sure that either the Right comes out on the first lead or you take the first trick. Never allow the enemy the chance to get that first trick and retain the Right at the same time.
On to the hand, yes the maker made a mistake. On 3rd street the maker, S1's team is down 0-2 in tricks and S4 plays the KS. The maker now has a choice here: throw off on the KS hoping his P has the AS or is void and trumps in or the maker can "trump high, send high, lead the QC which is effectively a 2nd boss club since the KC was turned down". When given the choice between gambling on two offsuits (KS vs QC) the maker should gamble on the turned-down suit as that's the suit his P is most likely boss in.
What's more here is the maker doesn't know if the the KH trump card is in his P's hand, S2's hand or the Kitty. That's something else the maker has to worry about should he play off on the KS: the 2S having that KH. But the maker never has to worry about that possibility if he just correctly trumps in and leads trump and leads the turned down suit QC. And here's yet another point to consider. S4 leading the KS is scarier than normal in this spot becuz if S4 had ASKS in this spot he would lead the KS every time here. So S4's KS lead could possibly be a hidden boss lead designed to trick the maker into throwing off. So S4's KS lead is a stronger KS lead than normal giving the maker even more reason NOT to gamble and throw off on it.
Cliffs: the clear correct line for the maker is to trump the KS, lead trump, and lead the QC. Gamble on the offsuit your P is more likely to be boss in, the AC can always be in the Kitty too.