The vast majority of women will not have their water break until they are at the hospital. I had all 3 of my kids water break at the hospital, and considering my last labor was less than 2 hours long, from start to finish, I would consider the lady in the theater an odd ball.
I was at the movies a few days before my middle was due, and would have never thought not to go because I was close to my due date.
I don't think the couple was wrong in asking for a partial refund, I do however, think the manager was being an SS for his attitude. He could have simply said yes or no.
If they had been denied the refund, and then gotten angry, that would have made them the SSs, but not because they asked.