I've seen an interview with one of the advisors of the show. He said that hoarding isn't just about numbers. It's about having more than you can manage to the point that it is out of control.
He said if you could keep 100 cats in a controlled, safe and clean environment, it wouldn't be hoarding.
I wish I could remember where I was that. I think it was on some news channel and the guy was promoting the new season.
That's how I've always defined hoarding in my head. It's good that an adviser for the show shares the same thought.