What Free is describing is a vulnerable stopper squeeze. These work "automatically" when you have two losers left in the hand (as compared to a "normal squeeze" where 1 loser is preferred). In this ending,
it works with only two winners in the five card ending BECAUSE South is squeezed in THREE SUITS instead of the normal two suits.
What happens is just as Free described. East runs his winners, coming to a four card ending (after AK and club at first three tricks, and East wins the third and runs 5 spades). This ending will be something like this, lead in West. When west leads the
♠A, east throws a heart and what is South to do? If he throws the heart ACE, East wins two hearts, if he throws a diamond, EW win the
♦A and
♦Q and if he throws a club? He is thrown in with a heart. After he cashes his last club, he is forced to lead away from the
♦K, setting up the diamond queen...
What you have to do as East, is figure West held 7 clubs (that is certain after 3 rounds of that suit), the heart ace and the diamond king. When he follows with exactly 2 spades, and if he thows away one heart and one diamond, to keep a clubs, you have to play for the
♦ king to be stiff, so you should get it right, no matter how he plays. Sometimes the "early" diamond discard will trick declarer, but not this time.