Suffice to say: There are many different methods for sending money. Some of them will involve paper forms, some will not. Some of them involve the internet, some will not. And each one has its own rules.

"Maybe the scammer wants the part of their money returned using a different method (one that does not allow cancelling, or has shorter deadlines)"

This is essentially correct. I've read about similar scams, and I believe this was how they worked.