I think what they mean is that if I'm making $1/month contributions to 20 different creators, and they're all on the same platform, I can pool that into a single transaction with a single $0.50 fee, meaning that fees eat only 2.5% of my donations.

If I were donating to creators on different platforms, it would be 20 transactions, each with a fee of around $0.30, so fees would eat 30% of my donations.