I don't think the actual technical "how" is of much importance so the article doesn't spend much time on it. They communicated effectively, and more important openly, over company boundaries. Many tools would have worked for that.

This is about "how" they banded together to reduce their disadvantage compared to the big cloud providers that had advance warning and insider knowledge/access to the vendors long before the rumors started.

Correct. It's the ability to share documents and conversation snippets provided by vendors, as well as curating and summarizing the significant amount of information available.

I've never seen an exploit that involves microcode updates, compiler fixes, kernel patches, and KVM/Xen updates all together. The number of moving parts is staggering.

Being able to filter and summarize that across company boundaries has helped me both understand and more effectively work to mitigate this problem.

And now there are "Tier 3" companies that didn't get invited to the slack channel.

It all helps big get bigger and making life harder for smaller companies. Not a great setup for a healthy competition.