Hermione hadn't meant to wake Ron up, how could she when she wasn't even aware that he was home? But she felt slightly guilty for doing so all the same. About to apologise and turn the light off again, his mini tirade distracted her for a moment.
"I was at my parents," she explained. "I walked home." She couldn't disagree with his assertion that it was freezing out there; she could feel it all the way down to her bones. But she was too thrown by the fact that he had moved across the room and wrapped his arms around her to say anything in agreement.
He was warm as he leant against her, and it went some way to thawing her out. "You smell like firewhiskey," she informed him quietly. One guess what he had been doing then.