This is an important question. You did nothing wrong, they'd like to hire you, but there was just something about you that made them hesitate. And because they have a ton of candidates for very few jobs, that hesitation means moving on. But it's NO knock on you - it's just some tiny thing that they probably should have ignored, but because they're focused on making a decision, they'll use any excuse to eliminate you. Don't think another second about it.