why is my location 600 miles away from me when i sign in to my apple id

Because that’s the physical address associated with the IP address you’re using as designated by the ISP, and because it’s more expensive for the ISP to be more accurate with the address, and because better accuracy is hazardous for users. IP addresses are best considered to be correct when they’re in the same country.

What if I don’t recognize the location shown in my sign in notification?

When you sign in on a device, you’ll get a notification on your other trusted devices that includes a map showing the approximate location of the new device. This is an approximate location based on the IP address the device is currently using, rather than the exact location of the device. The location shown might reflect the network you're connected to, and not your physical location. https://support.apple.com/en-us/HT204915