That's not how a VPN works. A VPN masks the information you are actually accessing by showing you query the VPN instead.
To make a connection to a service you still need an address. This info is what they are using to identify your device.
Most traffic is already encrypted (httpS) so someone spying on you wouldn't know the content of your communication only who you contact. But without a VPN a man in the Middle could see who you are contacting. E.g. looking up pornhub. With the VPN it only shows you looking up the VPN.