I think that means there's at least one kbin.social account who follows that Mastodon account, or at least that those posts have been boosted by accounts followed by Kbin users. As a result, kbin.social would've generated a local profile for that person so you can see the posts of his that have federated here. Similar to how when you use Mastodon, you can see a version of accounts on other instances' profiles without leaving your own instance.
exohuman