So when is a movie a TV series? Did you think of it as a movie or was your brain thinking TV?
It felt like a movie from the get go, in part because the lead is a movie star. It also clocks in at around 120 minutes total, which made me assume it was a movie.
Beyond that, it has become harder to define what makes a story a movie verus a tv show. We watched a two episode Agatha Christie murder mystery on Prime. If they had cut out the recap at the beginning of episode two and merged them together I would call it a movie.