It's confusion over the terminology. There are two definitions of "foreign key" in wide use: (1) When one table's key occurs as a value in another table, in th

It's confusion over the terminology. There are two definitions of "foreign key" in wide use: (1) When one table's key occurs as a value in another table, in that second table that column is sometimes called a foreign key. For example, table A has id, table B has A_id, and people refer to A_id as "a foreign key". (2) When you define this relationship explicitly in the database, so that the database can enforce it (and/or to document it), that's called a "foreign key constraint" but also sometimes just a "foreign key". This article just means they don't use #2. It doesn't mean they don't use #1. The phrasing was probably clearer in the context of the discussion they were having at the time because the comment above it linked some docs for the software in question (qh-ost), and under the "Limitations" section, those docs said, "Foreign key constraints are not supported." So to them it was clear they were talking about database constraints.