what do you mean how can you route without an IP address? they have one, internally, in the ISP's WLAN, they don't have one that can receive inbound connections.
you don't need an IP address on the internet to make connections out, CONNTRACK on the router handles the internal routing without that.
how it looks is the user has an IP address in common with dozens, maybe hundreds or more other users on the same last mile route. this can be in front of a mobile network as equally as a wired network.
it's getting less common but i'm sure there is still shitty ISPs that don't own enough IP addresses to give all of their customers their own.