Castiel was a little confused but not by his surrounds. Sam wasn't acting like he had last time he saw him. A girl who was closer to reaper than human teen had been drawn to Sam and Dean was nowhere to be found. He didn't like it. Of course, he hadn't liked the situation he'd been in before either but he'd understood it better.
Castiel was determined he needed to get back but, for now, that wasn't an option and he had things he needed to do. Both Sam and Lydia needed his assistance. He was determined to give it. Sam because they were friends (and because Cas took on some blame for Sam's situation) and Lydia because she interested Cas. He'd not met anyone like her. In part, also, because she had been trying to help Sam too.
Castiel knew Lucifer was in Sam's head. He didn't know how to get him out if it (yet). He didn't know about the wall. He didn't know he'd brought Sam back without his soul because, for him, that discover had yet to be made. He only knew Sam was suffering an effect of his time in the pit and there was no one else Cas knew of he could call on. Only him and, it seemed now, Lydia.
The girl had been easy to find. Only Sam and Dean were hidden from him (and all of their brothers.) He appeared behind her, placed a hand on her shoulder, and delivered them both to Sam's living room in a instant, without warning. His other hand held a six-pack of the promised beer.
He took his hand off Lydia's shoulder and it was only then he chose to address them both. "Hello Sam," he said simply but with relief in his voice. He turned his head to Lydia. "It is good to meet you."