Imagine your hand:
10 solid Spades, that will make 10 tricks in Spades trump, right? So what if we open with... 4♠?
You see that you're not sure to have 27 HCP on your side to play 4♠ normally. But you have lots of Spades, so it will work.
Now, look at the 4 hands that day:
In East-West, they make the grand slam in Hearts, Diamonds, or Clubs (look at the suits one by one and add the sure tricks: 5♥ + 4♦ + 4♣ = 13 tricks). But how can they bid them if you open with 4♠?
They don't have enough room to exchange information, so they will have a lot of trouble bidding a grand slam (and thus scoring the biggest bonus).
Your 4♠ is a preemptive opening: a high bid with a long suit and less than 10 HCP, to inconvenience the opponents. And the good news is, the suit doesn't need to be solid, it just needs to be decent, like with an honor. More precisely:
Two players each have 7 HCP. One has seven good Hearts; the other has a 4-3-3-3 hand. Which one has a hand suitable for a preemptive opening at 3♥?
Section quizYou have a weak hand with six good Spades. Which preemptive opening do you choose?
Section quizYou just learned 10 openings at once: a worthwhile read. So stay with me a little longer.
It's up to you to disrupt them as much as possible.