As I understand it there are several ways to shoot night scenes.
1) Actually film at night, with fast lenses.
2) Film at night with lighting that looks like regular night sky glow
3) Film during the day with filters that expose the film in such a way as to look like night.
4) Film during the day and process the film (called pulling X stops) so it looks like night.

The last two are usually pretty easy to detect as the actors have to squint a little in the daylight.

It's all interesting stuff.