Orthodox Christians vs Catholics in “Last Christmas” (UK, 2019)

Do you know what religions most Croatians are? Mostly Catholics. According to the latest census at least 85% of them. Hence I got a little confused watching “Last Christmas” written by Emma Thompson, staring Emilia Clarke. The opening scene is set in a beautiful Orthodox Church in the 1990’s Yugoslavia, where the protagonist sings (in English?!) as a young girl. We know it is Orthodox, because the camera lingers on for quite long on the elaborate iconostasis, a central feature of Eastern Orthodox churches.

The rest of the movie is set in present day London and she is a grown-up. Although there are some doubts  how adult she and her behavior is. Later we learn that her family’s ethnic background Croatian.  So why did the movie show a family, that is most likely Catholic  in an Orthodox church? Any ideas? I think it was just a lack of attention or hiring an expert.

(Apart from this, religion plays little role in the movie. There is a strong Christmas theme, obviously, a nod towards Hanukkah and a generally interesting mix of ethnic backgrounds.)