It isn’t so much that the pubkey is linked to a social media account, but instead the pubkey key is linked to a user-friendly name-somewhat related to the format of a name@domain. Here the name is the user friendly aspect and the domain is what verified the link between the user friendly name and the pubkey. There is a nostr NIP compliant file at the domain containing the link between the user friendly name and the pubkey. Before sites will include your name pubkey combo on their domain, they want some verification who controls the pubkey. This is often done by posting your pub key on Twitter, presumably doing so shows you control both. If you do the name/pubkey link on you own site-one can see who controls that site. I think this is an accurate description. Definitely interested in someone has a better characterization.