Ok, maybe let me put it this way. When you visit a website, you send a request to see the website and the website responds with the webpage. Now the request goes something like this.. From your computer -> your router -> your
ISP router -> ... -> website server
ISP router -> website router -> website computer -> website.
If you are using a router to connect to your
ISP, your computer will probably have a local
IP, but your router will have a public
IP. This public
IP will be sent all the way to the website, and will be used to get the response webpage from the website back to you. So the website will always know your public
IP.
Now each hop in the chain above will have a different MAC. Maybe, now the last hop MAC makes sense.