When you sort by the Vendor column, a file may look out of place when it's associated with multiple vendors. Go ahead and expand the Vendor field: you'll see that the file is sorted by the first vendor listed even if that's not the vendor displayed.
So how do we decide which vendor to display? We prioritize the vendor based on the file's relationship with a product line. So if the file is associated with a product line, the vendor associated with that product line is the one displayed in the Vendor column.