Ben isn't that bothered by Worf's screaming - but he doesn't realize it's a person first.

Instead, he gets up to go look for the source of the sound. He's got his "Earth clothes" on, his usual outfit of choice when he's going out drinking or wants to avoid drawing attention to himself. Whatever's going on, someone's upset, and he's going to go do something about it.

When he finds Worf, he asks the Klingon what's wrong. An alien, but not one from a species he knows.