This is a reference to the Cubs having been down three games to one and to his own team's abject squandering of a 3-1 lead in the NBA finals earlier this year that allowed Cleveland's Cavaliers to win. The Warriors' failure was partly due to Green's own fragile temperament, which got him suspended for Game 5.
So in the midst of the uncontrolled hat-tossing and ululating, here was Green wryly offering Cleveland (not much) sympathy and a touch of pained realism.
Many appreciated his mental agility. At the time of writing, his tweet has already enjoyed more than 105,000 retweets and 106,000 likes.
As a Warriors fan, I can only hope that next year's NBA finals won't be as close. And, by the by, congratulations, Cubs. You have a lovely ballpark. The food could do with improvement, though.