Careful. The author is not using "data structure" with the standard Computer Science meaning, but as C language struct. Standard data structures were actually the equivalent to current classes and were associated with a set of functions.

If you bother to take a look to C APIs, you'll find the familiar "handle" parameter, equivalent to the "this" or "self" of OO languages. Setting aside all the philosophical mumbo jumbo, OO is syntactic sugar over those interfaces.