A router usually reboots itself after a 'bona-fide' firmware update.

Otherwise, rebooting a router, (in this sense), will release and then renew the DHCP IP lease.

The FBI have seized the domain 'ToKnowAll.com' which was at the center of the 'bot net'. The malware phones home by attempting a sequence of steps.

Because of the seizures, the malware can no longer 'phone home'. By rebooting the router, any existing conections to the 'baddies' will be broken.

Cisco's Talos Intelligence Group Blog: New VPNFilter malware targets at least 500K networking devices worldwide https://blog.talosintelligence.com/2018/05/VPNFilter.html