I just checked the two independent bookstores nearest me and neither one of them has any mention of it in their online presence. I've been a frequent customer of independent bookstores for years and never heard about this before. There's no Wikipedia page and Google Trends tells me there's not enough data to even give me a search history for this.
It makes a great headline and I'm sure the people who organize it are annoyed, but this might just be a case of ant meet boot. It's weirdly reassuring for organizers to think that Amazon specifically targeted them, but it seems more likely that they just... didn't even know it was happening.