When you play the "Blind fold game", with your wife agreeing to DP with your best friend, she has to guess Who's Who, just by feel. She knows the rules, that if she guesses correctly, both men are allowed to cum inside her. And here she guesses correctly. She even says, "Your friend is in my pussy and you're in my ass".
That's a signal to both men, they don't have to hold back. And she prepares to take both loads, hopefully simultaneously.