People upvote questions for all kinds of reasons. They might think it's interesting. They might want to give the asker reputation (yes this happens). They might think it's a good question for the beta. Or they might have just seen a kitten and are really happy.
The point is, people vote however they like for whatever reason. Score is absolutely not to be taken as a strict indicator of quality.
Closing, on the other hand, is a more concrete process. There are close reasons. If a question fits one of these reasons, by all means close it.
Don't take into account score when voting to close or leave open a question. Just look at the content and make your decision from there based on current guidelines.