wan is techincally evening, so wouldn't good evening also be a possible answer?
Good evening would be 晚上好.
The difference between evening and night is non-existent in Chinese. 安 (peace) actually implies that you are going to sleep and will have no more activities.
Elsewhere in this lesson, they've been using 早安 to mean good morning. That doesn't sound like no further activities! :–)
But 晚安 is what you say to people when you are parting ways for the night to go home and go to bed.
It's pretty common in Chinese for one word to mean several different things. 吃饭 can mean "eat rice" or just "eat".
The pronunciation sounds a bit weird with the n' s pronounced very softly. Is it on purpose?
To me it even sounds like Wǎl'āl. I'm reporting it ... unless somebody tells me that it's just the guy's accent.
OK. Here is the skinny: syllable final "n" is often realized as a simple nasalization of the preceding vowel, just like some other languages such as Portuguese or French. [wan an] becomes [wã ã].
"Good evening" is a kind of "hello," in English, while "good night" is a kind of "goodbye."
晚安 is a "goodbye."