Neither one looked ahead and decided, "you know, maybe passing while there's oncoming traffic isn't such a hot idea"? Good for them

They're as bad as the guy in the compact truck who tried to pass me last weekend coming around a blind turn. I had my arm out and hand spread, giving him the "hold off a minute" signal because I could see the construction truck coming around the other way. He got right up next to me before realizing I had a good reason to hold him back, then had to slam his brakes and swing back into the lane. If he rides a bike, he probably does what you saw on the MUP, too.