Help me understand the source for the library view column 'Shared With'

Hi all,

I noticed that in a document library there's the option to customize the view to show the column 'Shared With'. However, I can't discern where it gets its information from. I was expecting it to show the unique permissions assigned to the folder/file but it seems that's not the case. See this example:

The column tells me that folder '1' is supposed to be shared with Test User. However, when I go into the details pane or the user.aspx advanced view this user does not show as having explicit permissions to this object. I verified this with multiple files/folders. It never seems to match the actual unique permissions assigned to they object either directly or via a sharing link.

Is anybody able to explain this and where 'Shared With' pulls its information from?

Thanks.