What is a "sharing only" account in users and groups settings?

I recently found an old friends name under "sharing only" in users and groups. I can't see this account when I go into the login page. What does this mean? I don't really trust him anymore so I'm not sure if he put something on my computer when he had access to it a long time ago. Screenshots are attached [Advanced settings for the account](https://preview.redd.it/zwgukaysti7e1.png?width=483&format=png&auto=webp&s=00d43e72fab9d1eafe201113fb84e5e9a3ffdc39) [The users and groups main page, with me as the top account](https://preview.redd.it/11vojaysti7e1.png?width=472&format=png&auto=webp&s=d0b2a201e70945431208c2b83e6b43b000cf509e)