AGPL is a “weak” copyleft license, not strong. It basically means not all derivatives need to be open sourced. If you modify AGPL code but never distribute it or provide it as a service over a network to users, you don’t have to provide source.
But the point is that they acknowledge that they forked Kibana and why. It’s no different than if someone forks Apache code to form a proprietary software company. The permissive license contributed to the success of many companies. They further acknowledge that Apache based Grafana can be forked too, but they’re betting on themselves to continue to succeed long term by focusing on good software, branding and community. The GP’s point seemed to indicate that “no one” acknowledged the Kibana origins when in fact Grafana themselves have.