This is orthogonal. Many languages traditionally considered functional do not enforce referential transparency, and nothing prevents you from building referentially transparent functions in an OO language.
Not speaking specifically about this situation, but just because a language considered functional implements a certain behavior doesn’t mean the behavior is functional. The causation usually works the other way. It’s because a majority of the behaviors a language implements are functional that the language is considered functional.
As an example, you can write procedural code in Java, which is the poster child of OOP programming. That does not make the procedural code OOP.
