They wouldn't just be giving in, it would take less than a day to get up and running on CloudFlare. That is probably worth avoiding $30k bill, especially for a non-profit.
As for PR, there absolutely is good will towards organizations that take on censorship. This is the #1 story on HN, so a company stepping in and saying "we got this covered, free of charge" not only shows they are good people, but also gives would be customers an idea of the quick implementation cycle for their CDN + the load it can handle.
Real world use case + helping to stop censorship = great PR
This is exactly what I was thinking. I read the blog post, then came to the comments. I completely expected something along the lines of ... "Hey, I'm the VP @ SomethingTech, we like what you're doing and will help you mitigate the attacks for free if you get in touch with us." ... to be the top comment here.
My reaction was based on the interview where they say that the 30k$ charge was harming, not killing them. You're more knowledgeable than me on CloudFlare and it may very well be a strong option.
Now in a way their $ penalty with this attack is not unlike growth. To me it sounds like they invested in their branding and will have a name as a company that can sustain damage and keep its ground - important because their goal is to be credible in bringing content in/out China.
What if they had given in? They'd be yet another victim of an attack sort of linked with China.
I do see a business sense behind what I assumed was their moral stance and I definitely stand by it.
And pretty certain that there's zero PR value in those stories.