I don't know how much better Juniper's stuff is, let alone Cloudflare's specific setup, but classic Cisco IOS gear's approach to batching, pretesting and merging configuration changes on mission-critical network infrastructure is basically "f*ck it, we'll do it live on the command line". Real '80s stuff, not far removed from "classic" Unix man-with-a-beard-and-a-Telnet-session configuration management (though the command line largely keeps outright syntax errors out of the config, and the (Nearly) One Big Config File makes basic restore-from-backup relatively straightforward.
Used to work on a bbone at an ATT competitor, used Juniper in the core. There was a lot of talk and sales too about SDN and the future of networking being all automated, but in the end there was always problems that needed a brain and an ssh session to fix
Any other tool that allows you to announce connectivity will have the same problem. In this scenario it was still even legitimate routes, it just was too much for their specific link to handle.