Yes and no

The Telco can say between what antennas you are. In urban areas with lots of antennas that’s still pretty accurate to almost say what building. Especially with 5G the number of antennas and accuracy go upto in some cases centimeter/inch accuracy so better than GPS. That last case would be in a mall with small antenna in each corridor.

In rural areas with data switched off that’s more like somewhere in that square mile, way worse than GPS.

You have to think of lemmy.world as your lemmy provider. Just like with e-mail you have your own email provider from the ISP, or gmail, or … If your own provider is down, you can’t receive or send mails, but all other people can send mails to each other. It’s the same with lemmy, but then for reading posts and send comments to that instance/provider.

Because they’re on lemdro.id as lemmy provider, not lemmy.world. That’s the @ part in the user name.