Has he tried unplugging the router for 15 minutes and plugging it back in? I jest but I know Comcast and Spectrum will both issue a new IP address in that timeframe.
Once the IP address I don't own is released and assigned to some other router how do you think CF determines the new IP address for the individual/home? Unless this person is running the CF Dynamic DNS service which gives CF the IP address, I'm not sure CF would have any reasonable validation techniques to determine who is what given the size of residential networks.
I had to use a VPN (a whole new IP) and clean chrome install to bypass one those "IP blocks" which was combined with fingerprinting.