CF had their route covered by RPKI, which at a high level uses certs to formalize delegation of IP address space.
What caused this specific behavior is the dilemma of backwards comparability when it comes to BGP security. We area long ways off from all routes being covered by rpki, (just 56% of v4 routes according to https://rpki-monitor.antd.nist.gov/ROV ) so invalid routes tend to be treated as less preferred, not rejected by BGP speakers that support RPKI.
What caused this specific behavior is the dilemma of backwards comparability when it comes to BGP security. We area long ways off from all routes being covered by rpki, (just 56% of v4 routes according to https://rpki-monitor.antd.nist.gov/ROV ) so invalid routes tend to be treated as less preferred, not rejected by BGP speakers that support RPKI.