Well no, it's purely a property of the fact that the packet is addressed to the router.
If the packet is addressed to a machine on the LAN, neither RPF or NAT will protect you from it. "The Internet won't route to private IPs" only protects you if you have private IPs on the LAN, and even then it only protects you from people who can't get access to the network on your WAN interface.
Any way you dice it, NAT isn't providing any protection.
If the packet is addressed to a machine on the LAN, neither RPF or NAT will protect you from it. "The Internet won't route to private IPs" only protects you if you have private IPs on the LAN, and even then it only protects you from people who can't get access to the network on your WAN interface.
Any way you dice it, NAT isn't providing any protection.