He means you're a morally good person. You aren't a bad person, in other words. Now, depending on HOW he said this, he either thinks that's a great thing, or he's being condescending and means that he prefers girls who AREN'T so "good". Without knowing this guy, it's hard to say what he meant by that. But anyway, he thinks you're a good person, in all-in-all, so take that how you want to.