It just means that the speaker was in the doorway and the other person was outside, so he was looking outside the house towards the other person.

Just to add to Ruthi's explanation... The verb "look" doesn't require an object, so if we need to indicate the target of your observation, we use "look [at ____ ]". Although "look out" can mean a person is being cautious or careful of danger, this context has the person standing inside, watching something outside. So, it clearly means the person is observing something that is not in the house, but out. Basically, the whole sentence tells us exactly what "look out" means here.