Despite my product being a dev product, I instantly got a paid customer through AppSumo after the deal going live, despite it being private, and despite me not sharing it with anyone.
That's very strange, but apparently normal. I've talked to several others on Twitter experiencing the same.
It seems that although it's privately listed, people are finding it via scripts or something similar.
I just hope people don't refund, which they actually have 2 months to do. I also hope that people leave good reviews!