Honestly, this is the first time I've ever thought about it (Halloween is not a big thing in my country) but it could be as simple explanation... he had time to write the paper that night while the kids where out trick or treating.

As a coder, I can relate to finding weird times to do deep work. I can recall many times working on some side project when everyone else is out partying or having fun. It's often those quite times with no one else around to bother you that you get your best work done.