Two bettas in a cup... I WISH I could say that's some new news. But I've seen it before...ugh. Worst things ever. "Customers" definitely did that to them. I'm glad they're both fine!
I think a betta's blood is red? Not sure. I've only read "if your betta has faced physical damage, look for any pinkish water, or red streaks from his scales." I'm assuming the "streaks" is the blood, and the "pinkish water" is diluted blood. But really, YELLOW water? Ugh. I'll take your word for it that they were mortified and actually had feelings for the poor critters. ~