This is normal. Most modern broadband modems are also NAT routers, meaning, they get assigned one WAN/Internet IP from your Internet provider, and they are able to serve multiple private/internal IP addresses to client PCs/devices. Those internal IPs are only for your local network, they are not routable to the internet. The modem/router then translates each packet to the external ip, combining traffic for your multiple devices to send out using the one external/WAN IP.
I hope this helps.
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