This kind of nightlight is usually used at night, so that people who go to the toilet or get up in the middle of the night will not be blind. It can also be used for lighting when making love, which won't make the room too bright or too dark, and it can also have a hazy feeling and increase the mood.
Maybe your boyfriend thinks you have this hint in it.
But he's asking you, which means he's not sure himself, but one thing is certain, he's a little interested in you.