How does this affect anything?

It’s a momentum thing. one general strike won’t change the world, it’s the start of a much larger movement to get people to organize in socialist organizations like the PSL (remember socialism has always been fascism’s greatest enemy) and in unions. A one-day general strike is not a “perfect is the enemy of good” logic, it’s simply materially impossible to get everyone to rally in one week, or one month, or likely one year. It’s just a start and a show of strength.