I think it's reading a little much into a single post to say: Impossible task--> Doesn't care--> End relationship

It's not considering a host of possibilities: 1) He felt his only bargaining factor was exacerbating the punishment. Which he got called on his bluff... (oops)
2) He's illiterate and doesn't know how much 1 million words is
3) He is giving one of those 'I know you'll fail tasks' so he can give her the physical punishment she needs.