So is C language a functional programming language?

Definition of functional (from Wikipedia page you linked to): In functional programming, functions are treated as first-class citizens, meaning that they can be bound to names (including local identifiers), passed as arguments, and returned from other functions, just as any other data type can.

In C language you can do all that. But C is not a functional programming language at all. Neither is Hooks functional. Even assembly language has "functions" but it is not a "functional language".