Filemaker Databases and their attached documentation frequently use the terms "table" when they should say "table Occurrence".
I don't have that file to look at, but most likely, Bill to Contacts and Ship to Contacts are two table occurrences with the same data source table, Contacts. You can check this in the relationships graph by hovering your mouse over the arrow in the upper left corner of each box.
The difference between them is that you'll see a differnt field in contacts being used to match records.
If you'd like to learn more here's a link to a post I made on the subject: